-Installation-

Choose which mod you need and extract to C:\Program Files (x86)\Steam\steamapps\common\Fallout 3\Data.

Choose F3+DLCs if you have the GOTY edition with all DLCs. Choose the others if you don't have any/all DLCs.

-Uninstall-

Delete every Item Prefix ESM's from C:\Program Files (x86)\Steam\steamapps\common\Fallout 3\Data.