First things first the links to the mod sites wikihow has are mod repost sites and not a good idea. Try curseforge instead, it's safer, more legit instead of fake versions mods are available for and many other reasons.
Otherwise, what part are you trying to work out with the 'mods tab' There is the 'Launch Options' tab where you select Minecraft versions, you select the Forge version/make a Profile for modded versions of the game.
If I was making a tutorial similar to that Wikihow articles I'd put it like this:
1.Install Forge/Consider the Minecraft version you want your modded instance to be. If you want 1.12.2., go for 1.12.2, if you want 1.7.10 then get the 1.7.10 Forge. The main Minecraft Launcher Forge setup requires you to get it from: "http://files.minecraftforge.net/maven/net/minecraftforge/forge/index_1.10.2.html" to get Forge, from Adfocus (which isn't as infamous of an Ad site as Adfly). Then once you get the download (or download it and exit the ad site since you don't need to worry if you get it downloading in the background). Once it's downloaded, go to your downloads folder or download location. Double click the Forge method (I usually use .jar but go for either I guess, I'll be stating the .jar method in this example). A message will pop up, select 'Install Client', Forge will do it's thing and your done.
Many players use MultiMC or Twitch to avoid the ad site or just make mod downloads/instances of the game much easier for them. If you want the Mojang Launcher to stay for main versions of the game/unmodded go for that I'd say. But if you want to stick with the Launcher you got with the game and not Third Party Launcher like I mentioned I completely understand.
2.Download mods from safe sources like Curse sites.
Planetminecraft is sort of but it depends on the links as many creators can send you to ad sites that aren't safe. Any other sources like 9minecraft, Minecraftmods, 6minecraft and so on are mod repost sites and are Community Content Stealers/Community Content File Manipulators. There are a lot out there when you see the list of how many there are. Curseforge/Curse.com is safe and hosts community content with no redirections for downloads to the content or making you go through loopholes just to get content made by the community.
Remember the version of Minecraft/Forge you installed, mods for that version only work with that version, so if you wanted 1.12.2 and a 1.12 mod exists, 1.12 won't work but 1.12.2 will. It can be complicated but it's how it works unfortunately. An anomaly of this is around the 1.9.4 and 1.10 versions period for mods but that's only if developers supported that, otherwise it wasn't possible and not think mods usually work on any version no mater the .1 or .2 number differences.
Launch Options is the tab you want to select versions of the game, standard or modded. If you want 1.13.2 Vanilla/Standard, you select that, and the games Launcher (what your using to do this stuff) will download it for you. If you want modded 1.12.2 you need the Forge profile you just installed before. Most Forge versions installed appear below Release 1.0 (not the case for Forge 1.13.2, Rift Modloader or Fabric snapshot versions).
Look at the images below to understand what I mean. If I need to explain more let me know.
4.Put your mods into your mods folder.
Put mods into a 'mods' folder Forge may or may not have created for you in your .Minecraft setup that the main game already setup for you. Forge 1.12.2 and before allows for version folders in your mods folder, so if I have 1.7.10 mods but don't want it to read 1.12.2. mods I'll separate them so it can only read the 1.12.2 mods instead of the 1.7.10 ones. Make sure to not mix up mods it gets awkward if the mod file doesn't state the version it's for or otherwise. Core mods are also important. For example many mods use Core/Library/API mods to have core for multiple mods or spell things that are important. So you will sometimes need to get those as well as that the mod you want works. Some mods are optional on such compatibility but most are important.
5.Launch the game.
Once you have your mods, Forge and profile setup, you can play the game. If you get crashes, check the mods by sorting them to find out what works, what doesn't and if you missing core mods. If there is no issues, then the game will run fine to the title screen.
Launch Options generic
Launch Options - versions for 1.12.2 and below
Core mod versus the mod you want to run
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'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. I also make modpacks/maps
Creator/Maintainer of Fabric, Rift & Tesla Mod Discussion Threads/Niche Mod Youtuber.