Setting Up Your Environment - shauncjones/Community-Mod GitHub Wiki
Note: This tutorial is created on windows and commands may vary on other systems.
Install the JDK (Java Development Kit)
To develop Minecraft mods you must have the Java Development Kit installed. If you've already done this you can skip this section.
Installing the JDK is as simple as downloading the installer and running it. It can be downloaded from here. You must also set the "path" of the JDK. You can find a tutorial on how to do that here.
Installation of Intellij IDEA
You could write a mod in notepad. However, we are going to install a IDE (Integrated Development Environment) to make this a lot easier. You can download Intellij IDEA from here, simply run the installer and if you get no errors then everything is fine.
Setup of the Forge MDK
To begin setting up Minecraft Forge you must simply download it from here. For this tutorial we will be using Forge build 14.23.1.2555 for Minecraft 1.12.2.
Once downloaded simply extract the folder to wherever you're going to be developing, open a command prompt window in the directory you just extracted it too, and run gradlew setupDecompWorkspace idea
To make sure everything is setup correctly, in Intellij do the following: runMinecraft Client>run>run anyway.
Going Forward
You will see a mod package in the project called examplemod. We will be deleting that and writing our own in the next tutorial. Feel free to look around in the package to explore.
You can find the next tutorial here.