Since the other tutorial on this matter is riddled with insults and belittlement of other people, I decided to try to write my own based on my experience and what I know. I hope this is helpful, and any more equipped users can feel free to correct where it isn't.
Let me start by stating this tutorial is for WINDOWS. I don't know anything about Mac or Linux but I wouldn't object to someone posting a helpful tutorial on the thread. But I do have experience with Windows XP and Windows 7. (I assume Vista is similar enough o 7 that it will suffice for those who use Vista.)
Also, for clarity, installing mods does not involve the Mods and Texture Packs option on the Minecraft start menu. This feature is for texture packs exclusively.
So, you see a mod you like on the Minecraft site but you have no idea how to install it. You've never heard of a .jar file before, and you aren't sure what winRAR is because you've never used it. That's fine. If you've never had a use for these things, why would you know about them?
You'll need to install that. You just install it like every other program.
Now you'll need to find the Minecraft jar file. To do this, follow these instructions:
Open start menu
type in cmd (short for command. This will bring up the command prompt. That's the black box with white letters inside it.)
In the command prompt, type in “%appdata% and hit enter.
You should see a folder named “.minecraft”, open it.
Right-click the Minecraft.jar file (DO NOT DOUBLE-CLICK) and hover your mouse over “Open with”. (If this step doesn't work, try clicking on the jar file once and then right-clicking.)
Select winRAR o open the file.
Windows 7 (and possibly Vista)
Open start menu
Type %appdata% in the search bar at the bottom of the menu and hut enter
Open the file titled .minecraft
Open the bin file
Right-click the minecraft.jar file (DO NOT DOUBLE-CLICK) and hover your mouse over “open with”
Select winRAR to open the file.
I was also told this is an easy way to add mods for Vista, though some of these steps might also work for other Windows OS.
1. Open a random folder
2. Click nest to the location text, so it becomes blue and you can edit it
3. Type %appdata% and press Enter
4. Double-click .minecraft
Now I'm going to explain some of this. The reason you don't double-click on the .jar file to open it is because, by default, it will open in java. That won't do you any good unless you know java and know what you're doing. Opening it in winRAR gives you easy access to the files.
Saving What Matters:
Now that you have access to the location of the jar, I recommend you back it up, but in my experience, this isn't usually needed unless you have previously installed mods that you don't feel like reinstalling. (For example, I do back up my jar file if I have the latest Optimine installed because I don't fee like being bothered with reinstalling it again.) If you have never successfully installed a mod before, don't even bother. You should, however, back up your save files, as outdate or otherwise broken mods might result in losing your entire world. The folder containing your saves is in the same place as the bin folder containing the minecraft.jar. Just copy that entire folder and plce it somewhere you can find it if you need to. (I just plunk mine on the desktop. Easy access. :V)
I'd like to take a bit of time to point out that mods are not supported by Mojang or its affiliates, and virtually every update to Minecraft will break your mods, so I strongly recommend backing up your saves. Mojang and Notch don't take any care in accommodating modders when it comes to updates. They update vanilla (standard) Minecraft, that's the product they offer, that's the product they support. User-made mods are rarely taken into consideration and thus, you use mods at your own risk and at the risk of your save games.
Before you start downloading the mods you want, you should read the first post. If nothing else, you should at least read the known bugs, installation, requirements, and, if posted, block Ids. (I generally ignore the changelog unless something was removed from a previous version and I want to know why.) You should be especially aware of the known bugs section, because this usually lists bugs the modder knows about and is either trying to fix or unable to fix. It can help you avoid problems with your game. It's also a good idea to read through the FAQ if you encounter any problems specific to the mod.
Some mods require other mods to function. In most cases, the more complex (and usually more popular) mods will involve ModLoader. There are two ModLoaders on the forums, but most people use Risugami's. (I think it's because it's an updated version of 303's.) Usually, the first post will link you to other mods required. If it doesn't, you can usually find the most often used mods on the One Stop Mod Shop thread posted in the Mapping & Modding section. (That thread is now closed due to the OP's lack of time to spend on Minecraft, apparently, but the list still has useful links if you need them.)
If you encounter such a mod, you should install ModLoader, or other required mods before installing the mod that requires them to avoid trouble.
But before you close that jar file and try out your mods, be sure to delete the META-INF folder. If you don't, your game will instantly black-screen on startup. If you forget to do this, just go open up the jar file again and delete it. No harm will be done.
To actually install your mods, you'll need to open the .zip file containing the mods. In addition to the instructions listed here, some mods come with a readme file, usually a plain text file (.txt) containing extra instructions about where to place certain files or folders. I suggest reading the readme file before placing the mods into your Minecraft.jar or you might break something.
I's Dotted and D's... Curved?
Remember when I said to be mindful of the block IDs? This is becaue if two mods use the same block ID, one mod is likely to break another, or you might black-screen. If this happens, you'll just have to pick one mod over the other and post a (polite!) request on the thread of the mod for the modder to try making their mod compatible with the other mod. (Sometimes, this just can't be done, even if a modder tries their hardest because some mods need the same class file to operate properly. I urge anyone reading this to try to be mindful of this, even though it can be a little disheartening at times.)
If something does go awry, there are a few things you can do about it. The first thing you should do is get a clean .jar file. You do this by deleting your minecraft.jar and then deleting the version file. Now just run Minecraft.exe again and it should redownload the files for you. If it doesn't, also delete a file titled md5c and try running Minecraft again.
Now, depending on the problem, you should do one of the following.
If one of your default items, or the item of another mod, isn't functioning properly, you should begin to reinstall the mods one at a time and try out each until you think you've found the one that has broken something, then get a clean jar file (By deleting the old one as per the steps above) and try the mod on its own (if it's broken a default item, such as a bucket) or try the mod with the mod that it seems to conflict with. If the mod is, indeed, breaking a default item and its default purpose (such as picking up lava), you need to report it on the thread. Make sure to post a constructive reply that details, in a preferably grammatically correct way (Or, if English isn't your first language and you struggle with it, as grammatically correct as you can manage), about what you experience when trying to do something the mod seems to have broken. But before you go posting your problem, it's a good idea to look on the Known Bugs (or Known Issues) page and see if the problem has already been reported before. If your problem is on that list, then the modder is already aware of it and likely trying to fix it when they can, in this case, you'll just have to be patient and wait for an update.
If the problem is with another mod, it's likely compatibility problems, in which case you should refer to the suggestions above, try to convince one of the modders to make their mod compatible with the other. Otherwise, you'll just have to choose one.
Like a Version~Touched for the Very First Time~
If the problem is causing you to black screen every time you start Minecraft, and you've followed the instructions to the letter, it's time to go back to the modder's thread and look up which version your mod(s) are compatible with. If the thread doesn't say the mods are compatible with the latest version of Minecraft, they won't work. You'll just have to wait for a mod update.
You can check which version of Minecraft you have at the start screen in the top-left corner.
Covering Your Bases:
If your version is compatible with the mod you're trying to install, there could be a number of other reasons the mod isn't working properly. Make sure you have the mods the mod you're trying to use requires (Usually ModLoader), and make sure that you transferred all of the files from the folder you downloaded into the Minecraft jar. If you've done all this, it might be time to ask (Politely and as grammatically correct as you can!) for assistance on the thread.
If your Minecraft shows an error and a crash report, make sure you have the mods necessary for the mods you want to install to operate (ModLoader, usually), and if you've covered all your bases, it's time to post on the modder's thread. Make sure to include the crash report. Most modders won't even give you the time of day unless you post the crash report. This isn't to be mean, it's because it's hard for them to solve problems based on vague explanations like “Minecraft crashed” that could mean a hundred different things. The error report might look like mumbo-jumbo to you and me, but a modder is equipped to decipher it and pinpoint the problem for you (Given that modders usually know Java code and the error reports Minecraft gives you are usually related to Java.)
If you try to install a mod or delete the META-INF file and you're given this error:
Do the following:
-Press CTRL (control), ALT, and DEL (Delete) at the same time to bring up the Task Manager (That box that lists the programs currently running.)
-Near the top of the box, there should be tabs, one of which should be called "processes", click it.
-Look for a process called javaw.exe and highlight (click on) it.
-Click "stop" at the bottom of the box
-Press CTRL (Control), ALT, and DEL (Delete) at the same time. A list of five options should appear.
-Click the bottom option, which should be your Task Manager
-Look near the top of the box for tabs, one of which should say "processes", click on that.
-Look for a process called javaw.exe, now highlight (click on) it.
-Click "stop" at the bottom of the page.
(The instructions should be similar for Vista, unless I'm mistaken.)
Now try to modify your .jar file again.
(I actually encountered this problem when I first tried to mod Minecraft. I asked on this forum and another user gave me the answer. I would have never figured this out had I not asked because I didn't even know what to look for.)
If anyone does all of the following and still runs into trouble, I likely won't be able to help you. I've said all I know on this subject, and even when I follow these instructions to a T, I still run into problems and make mistakes. But I do hope this is helpful to anyone who would like a detailed tutorial.
Most modders copy/paste simple, short mod installation steps into their threads for all platforms. so if this long-winded tutorial confused you, and you'd just like a simple answer, you can likely find it in most of the reputable mod threads.
yeah i worked fine intell i deleted the file..... every time i try to open my chest minecraft crashes. nothing works now. GREAT AND THANKS!!!
You must not delete the mod files. It could be a modified class that already is in the game.
And when the mod is destroyed, and you have items in a chest that belongs to that mod, it is not weird that it crashes.
yer so i got everything i needed but when i tried to put the mod into to minecraft.jar file, nothing happens... it just wont copy over or something. i don't know pls help?
P.S. i downloaded mod loader but what do i do with it?
i tried following your instructions on how to install a mod
when i downloaded the mod, it opened with winRAR and i dragged all the files into the minecraft.jar winRAR.
this mod did not have a readme.
is this what i should have done, because the mod did not work. Thanks for your help