While having to individually install mods step-by-step can be a tedious process, the Fallout 3 Nexus is a phenomenal resource for both experienced modders and newcomers alike.
Most of these mods will be installed via the Nexus Mod Manager, an excellent tool used for managing and installing/removing the various mods that can be added to the game. The primary method for installing mods to Fallout 3 is via the Nexus Mods community, which boasts a massive library of gameplay mods, graphical overhauls and user-created content.