Welcome to Modding!
The first thing you want to do is to download a few things that will make decompiling, coding and modding Minecraft infinitesimally easier. They are:
First is MinecraftForge; download the src, also known as source, package.
(All links open new windows.)
Furthermore, you need JDK, or Java Development Kit. This allows you to edit Java classes and jars.
Lastly, Eclipse. This is what allows you to code classes for java. I prefer Eclipse but whatever you find attractive or already use is completely up to you.
After downloading, install JDK. After installing, you need to set a path variable to the folder you installed it in. Click on your start menu button, then right click on Computer and select properties. When that window opens up, click on Advanced System Settings and go to the advanced tab. At the very bottom there should be a button labeled Environment Variables. Click on that, and under system variables there should be a label called Path. Double click on it, and scroll to the end of the text. Then paste the text below at the end of the line, DO NOT REPLACE THE ENTIRE LINE.
;C:\Program Files (x86)\Java\jdk1.7.0_09\bin;C:\Program Files (x86)\Java\jre8\bin
Note that jdk1.7.0_09 will be outdated at some point. Instead, add a link to the newest version's bin folder.
The first part is the location of your JDK install. The second is Java. If you used a custom install for Java, give it the location of your bin folder. Also, if you use jre6 or jre5 change the path to fit your java version.
Now you're ready for the next step.
Unzip the minecraftforge zip file and put it on to your desktop. Next, hold down shift and right click on to the back of the file (don't click on to a file/folder). Select the option "Open command window here"
Type in the phrase "gradlew setupDecompWorkspace" without the quotes. Once that process is finished, type in "gradlew eclipse" if you're using eclipse. If your IDE is not eclipse simply type in the name of your IDE.
To recompile your mod, type in the phrase "gradlew build"
That will produce a reobfuscated jar file (inside libs folder) that you can then drop into your mods folder to test.
To set up your main file, the next step is here.
First is MinecraftForge; download the src, also known as source, package.
(All links open new windows.)
Furthermore, you need JDK, or Java Development Kit. This allows you to edit Java classes and jars.
Lastly, Eclipse. This is what allows you to code classes for java. I prefer Eclipse but whatever you find attractive or already use is completely up to you.
After downloading, install JDK. After installing, you need to set a path variable to the folder you installed it in. Click on your start menu button, then right click on Computer and select properties. When that window opens up, click on Advanced System Settings and go to the advanced tab. At the very bottom there should be a button labeled Environment Variables. Click on that, and under system variables there should be a label called Path. Double click on it, and scroll to the end of the text. Then paste the text below at the end of the line, DO NOT REPLACE THE ENTIRE LINE.
;C:\Program Files (x86)\Java\jdk1.7.0_09\bin;C:\Program Files (x86)\Java\jre8\bin
Note that jdk1.7.0_09 will be outdated at some point. Instead, add a link to the newest version's bin folder.
The first part is the location of your JDK install. The second is Java. If you used a custom install for Java, give it the location of your bin folder. Also, if you use jre6 or jre5 change the path to fit your java version.
Now you're ready for the next step.
Unzip the minecraftforge zip file and put it on to your desktop. Next, hold down shift and right click on to the back of the file (don't click on to a file/folder). Select the option "Open command window here"
Type in the phrase "gradlew setupDecompWorkspace" without the quotes. Once that process is finished, type in "gradlew eclipse" if you're using eclipse. If your IDE is not eclipse simply type in the name of your IDE.
To recompile your mod, type in the phrase "gradlew build"
That will produce a reobfuscated jar file (inside libs folder) that you can then drop into your mods folder to test.
To set up your main file, the next step is here.