Once you have made your mod, you want to export it to a jar file. Then add a file called mod.txt in your jar containing four, comma-separated values.

<Game Version>,<Mod Name>,<Mod Version>,<Main Class>

1. Game Version the version id that the game is running. Currently 1.
2. Mod Name Your Mod Name
3. Mod Version The Version of Your Mod (Example: 1.0.0)
4. Main Class Your Main Mod Class You Created in Step: 2.1 (Example: imdaveead.someclicker.examplemod.ExampleMod)