For Steam users, the directory is: Library/Application\ Support/Steam/steamapps/common/RimWorld.Right-click the RimWorld application and show package contents.RimWorld\Mods\Modfolder\Modfolder, when extracting your mod Make sure not to 'double extract' your mod, e.g.
This might be useful in saving historical versions or for playing offline. If you want to install a Steam mod manually, can help. Once you find a mod you like that is compatible with the version of RimWorld you have, you can download them from their individual threads. The main source for finding mods is the mod release section on the forums. Look online and find a mod that you want to try out. You'll learn where to install your downloaded mods and how to activate them, along with some notes on compatibility and backups.