It's super easy, just download and put the "World Edit" folder in your mods folder! That's it! (make sure to unzip the folder first if you are using the unmerged version!)
DO NOT put World Edit in a subfolder! It is a script mod and needs to be added to your Mods folder directly!
The Install Directory is usually locatd under:
Make sure you have enabled Mods in your game’s settings! Go to settings/other and check the little boxes “enable custom content” and “enable script mods”