tModLoader - A Modding API
Mod List Wiki Pages
Mod Links
Instructions
Unzip the tModloader zip file contents into the Terraria installation folder. E.g. C:\Program Files (x86)\Steam\steamapps\common\Terraria
Unzip the contents of the mod file zips into the Terraria\ModLoader\Mods folder in your My Documents -> My Games folder. E.g. C:\Users(Your User Name)\Documents\My Games\Terraria\ModLoader\Mods