This launcher contains a selection of modpacks that add a varying experience to the vanilla game. This ranges from magic to machines. I would suggest that you do some research about these modpacks and choose one that suits the experience that you are after.
They can be daunting at first but are extremely fun!
JourneyMap adds minimap with radar, full screen map, waypoints. A must.
Just Enough Items (JEI) especially if you plan to try content adding mods.
Light level overlay. Insanely useful for lighting up places.
The content mod I been into lately is Abyssalcraft, based on HP Lovecraft stuff. New biomes, materials, ores, monsters, several more tool/armor levels over diamond (you'll need them), 4 additional dimensions, new machines (i.e. crystallizer), a whole new energy collection system, rituals, etc. Good stuff.
Ease From Vanilla to Mods for Version 1.12.2 using Forge (Forge is the mod tool/modloader that allows compatibility between mods and Minecraft to work well together, but has a lot of developer features which is why biomes, machines/interfaces, fluids, mobs and a lot of other possibilities are so crazy or great with mods):
I tried to go for variety to ease in to mods
(-from recipe viewing to find if too many items/blocks that mods add or just vanilla recipes,
-a minimap for exploration/places you have been in the past/teleporting straight to them,
-biome mods for a different experience,
-a few quality of life (small tweaks or things you can't live without I guess you could say),
-technology/tools/dimensions types to not only cover those areas but give you an idea of what you can do from using power for a furnace instead of coal/combustible fuels for example at first, to sometimes x2 ores, special crafting table blocks, power storage to maintain and refill, tools that allow for more durability, higher tiers than diamond to break blocks, faster speed, or with some mods customisation or different/similar benefits to the enchantment system in vanilla.
I tried to give a mix of multiple categories to go about each for the first time or just similar to Vanilla with a few twists, the others listing mainstream or big content mods doesn't seem right to me. A mix of any category to see which one sticks out to you of what options you have or preference of differences/similarities to Vanilla I feel makes more sense to me personally).
-JourneyMap (Minimap/WorldMap), I personally use Xaero's (more like what a minimap would look like if a Vanilla one existed) or Mapwriter since they aren't as computer intensive as JourneyMap but JourneyMap is a great mod (at least in my experience anyways).
-Biomes O' Plenty (biome variety, other bits and pieces of blocks to add to the biomes, you have to enable this mod with a 'world type' selection, think Default, Superflat, Large Biomes, that button, cycle until you see Biomes O' Plenty and you have those biomes in your world now upon world creation, this mod adds a lot of blocks and items though so be careful of your RAM usage)
-Light Level Overlay (think of it the same way you would a mob trap/farm, mobs spawn at different light levels, you use this mod not only for making it easier to tell the light level of say a torch which is 15, Glowstone is 16, and Redstone Torches are lesser on light level, but also ease of spawning mobs you might want (as in broking out say mobs like zombies, but allowing others that can still spawn to spawn) or just blocking out areas of a building/cave that has dark spots where mobs can still spawn, it's a great mod mostly so you can find the spots you missed that mobs can still spawn on I feel more so)
-LightningCraft (while not a mainstream mod that not many would recommend or know about, it provides, a bit of technology in a small way with Lightning power, (a golf club that strikes Lightning onto lightning rods called Air Terminals, has a crusher for x2 ores, faster smelting, a special crafting table block), a dimension with Underworld mobs and a bit of interesting loot from the mod, tools and powered armour, a bit of progression needed for the dimension access with demons you defeat in the Nether to access a blood item to craft the portal to the Underworld, I think it's the best, a 'bit of everything in one' type of mod and I use it a lot since it's a favourite of mine, but not many people would likely recommend it if they have never heard of it XD when I can see mostly mainstream mods listed here in this thread and being a niche mod over mainstream after playing mainstream mods for years or having less ideas for them and curiosity to branch out I thought my niche mod 2 cents could be applied here to give other options certain people haven't yet [not meaning it that mainstream is bad, just saying many don't know about them or use them, it's not bad people don't just some of them offer a lot of good things people just don't talk about and stick with what they know or rarely branch out unless its a modpack that happens to have other mods which 90% of the time it has all the mainstream mods with the odd few of niche]).
-Aether Legacy (want a dimension that's simple to understand/similar to The End, has a bit of a challenge and bosses, loot and a great mod if you want to start Minecraft from scratch again (wood, stone, iron tiers of tools and weapons and so on I mean) it's worth a go. It's based on Aether 1, not Aether 2 which is bigger, different and many ways and made by the main developers)
-Tinker's Construct (a good mod to recommend to anyone for their first mod to understand each category of mods, from tools creation/customisation of not just parts but also modifiers to improve your tools the way you would enchantments, technology easing into for understanding lava into the tank to use in the smeltery multiblock (think multiblock the way you would a nether portal forming to make something interesting happen next only can be more customisable on blocks and a different purpose to melt or mold things), can be automated with hoppers or redstone if you prefer to. Also as Tinker's requires a core/library/API mod called 'Mantle', it will help you understand some mods need core mods that have other code in them to be required to run, it's annoying but it's important to provide understanding of it besides what Tinker's does being great as well. I won't go into addons as they are based on a deeper modded player's preference and I never use them because they give me too much or don't have what I'm looking for personally.
-Extra Utilities or Actually Additions (great mods for adding lots of 'utilities' or a mix of anything from 1.machines/generators, 2.angel block that can be placed anywhere, yes anyways, doesn't need to be placed on anything, can in the air, 3.creative mode like flight ring [think is still in the mod], and good variety of items and blocks (Extra Utils), 1.to a growth ring for your faster crop harvesting/growing, 2.more food options, a bit of automation options canola seeds to canola oil to use oil for machines to crush ores/other blocks and items, faster/powered furnace, it gets really good with few tech stuff that takes a bit at first but is really helpful later on (Actually Additions). (these mods do get big be careful on RAM usage)
-Clotheslines (an item transportation mod that's also useful as a decoration XD it's been a more recent mod I've found interesting to use for item transport and fun getting past the fact it's yes a clothesline)
-Find Your Way or Ender Compass (mods that add compasses to find structures if you struggle to or want it find them without wasting time), Ender Compass only does Strongholds though, while Find Your Way does many structures. No dungeons unfortunately, but it does most of the others like Woodland Mansion, Stronghold, Village, Ocean Monument & Nether Fortress (only 5 at the moment). Also forgot Magical Map too.
-Better Builder Wands (makes building easier with wands which allow for rows/columns of blocks to easily be placed if you understand how as it can be a bit awkward at first). Another mod in a similar vein I'd recommend is Direwolf20's 'Building Gadgets' which is going a lot of interesting directions and the creator is a Youtuber that is big and focuses on the mainstream mods but is usually a good person to assist people into technology focused mods or not into mods at all but more so the technology side of modding.
-Quark (while I'm not big on this mod myself in use, I see the appeal for it with more vanilla focused blocks, items and things about it that makes it a good introduction to mods with Vanilla like similarities or wants it makes sense to be a recommended choice that aren't in Vanilla but still have a Vanilla feel, it is big though so be careful on RAM usage)
-Spice of Life (a mod that in modpacks works annoyingly well with AppleSkin, think of this mod as a 'variety of food you eat matters' situation/mod, food choices are now the important part and you need to swap food to get more out of it as well as keep the game interesting, I personally hate this mod, but for a twist on the hunger bar and food to change things up it's worth a go for challenge or just a go for something like it which is more what I'm recommending it for then it's up to you if it annoys you)
-Storage Cabinet (good for either more of the same item like a barrel mod, or enchanted books/NBT items, NBT focused items or blocks are stuff that's more so only able to hold 1 of itself rather than stacks of 64 or 16).
-SimpleHarvest or Reap (they do similar so, and due to Reap for 1.13, SimpleHarvest for 1.14 besides 1.12.2 and below versions) (these are right click harvesting crop mods, instead of breaking and replacing you do things even quicker by harvesting on right click XD we mod community players love to make things so small just so much easier even by a bit, but it's worth it sometimes like a mod in this case)
-Waila or TUMAT or WIT (these mods have 1 thing in common but differ a lot in features, these mods I like to call 'Inworld Identifiers' but they basically just allow the player to 'depending on the mod and it's features' can state the mod the block is from, the health of mobs, the pickaxe tier an ore is, the fluid (water, lava, a modded fluid like Oil) and how much is stored in a fluid storage container, some state how much is inside a chest for the types of items in it. These are very helpful if you don't know the mod a block is from or the pickaxe tier to mine them if iron or diamond might work but modded picks might be needed for some tiers and finding out which one isn't easy, more so than the other features as that's more what other modded players use more or need them for I feel at least about them. But otherwise the mods vary in features so go for what suits more. Waila adds a lot but it's not always been great for me since it has so many addons or gets awkward for game memory for me at least so I recommended the other options as alternatives as good as Waila but not perfect as Waila)
-Aquarius (a few aquatic like blocks and features)
-Nether and End Ores (vanilla ores in the nether and end, great for x2/x3 ores the way you would for silk touch only you have to find them in the dimensions as the challenge compared to just x2 in a tech mod grinder/crusher), while 1.12.2 has a few of these I think 1.13 it suits to recommend since 1.13 focuses more on vanilla-ish mods.
-Rift: Corail Recycler (an uncrafting mod)
-Patty's More Tools 2 (more tools with varying blocks to use besides just ores)
-Half Logs (stripped log and log stairs and slabs, it's a building mod/Rift Modloader test mod in a way too)
-Stockpile (a barrel mod, barrel mods are good for large stacks of blocks/items, think lots of cobblestone in one place, these are great, probably almost as good as hoppers used as buffers I guess)
-Gamemode fix (not a fan of the gamemode numbers being gone and /gamemode creative needs to be typed every time, well the 1.12.2 gamemode 0, 1, 2 & 3 are back in 1.13), another mod like this for 1.14 snapshots works similar called Gamemode numbers, it does 0, 1, 2, 3 and S, SP, C, A short of the words but with only the letters like you used to with 1.12.2 and before 1.13)
-WorldInfo (identifies blocks in the world)
-Rift: Wastelands (a biome mod, not as great as Biomes O' Plenty but Rift Modloader has limitations or differences compared to Forge which for mod devs has a lot of options to make crazy or brilliant ideas no matter how big or small)
-Neat: for Rift (Neat mod health bar for the Rift Modloader/1.13 mod environment)
Rift mod search since 1.13 mods are all/sort of all, Rift focused right now:
That's my options, if you want Forge/Rift tutorials many exist out there. But if you want to start simpler and don't know how to use Forge/Rift and want just simple modpacks to get you started. Try a few Lite/Simpler modpacks with very little in them. Modpacks can get really big and huge on content. So it's best to go for Lite ones and allow not only for how many mods but the types of mods. Modpacks get big and you need more RAM to run them the more heavy content focused ones their are and how many blocks, items, and extras are added which is why I didn't recommend too many big mods and more so went for big mods if I though for variety sake and category they were the best choices. I make my own to pick what I want and management my RAM so I'm used to Forge & Rift these days over Modpack, but I don't see modpacks that are made by someone else as bad usually so I look for mods often to know what's new, what suits me that day and so on besides the 'big mod' recommendation that don't suit everyone. Just too many of the same mods are used or knowing the right one isn't easy sometimes. Especially if your mod preferences are like mine and rarely are the niche mods in those modpacks besides I guess JEI as my go to recipe/cheat mod, otherwise I go niche or otherwise for mod testing mostly these days.
'Niche Community Content Finder' for fun and support of creators. I just swim through my 'Experimentation Pond' of content that intrigues me or really needs a bit of acknowledgement or bug fix testing/reporting.
Creator/Maintainer of Fabric, Rift & Tesla Mod Discussion Threads/Niche Mod Youtuber.