Generally speaking, mods exist in individual folders located in the "Mods" folder of your WASTED installation. Within each Mod Folder are .WMD (WASTED Mod Data) files (which are essentially just LUA scripts), and any other assets/assetbundles that need to be used by the mod. Some Mod Folders contain a load_order.cfg file if the order in which the script files need to be executed is important. (See the Load Order page for more information on that).