The Fuel Loader is a machine that is necessary in order to supply fuel to any type of Rocket or to a Moon Buggy. To use the Fuel Loader, it must be supplied with power (either by wire or a battery) and Fuel from a Refinery. It must be placed directly next to a Rocket Launch Pad or a Buggy Fueling Pad.
There are two methods of supplying the Fuel Loader with fuel: The first method is to place a Fuel Canister (or other fuel container such as a BuildCraft fuel bucket) inside the loader which will empty the canister and partially fill the loader's internal fuel tank. The second method is to connect pipes from other mods such as BuildCraft and pump the fuel into the loader directly from a refinery. Once there is fuel in the loader, place your rocket or buggy on its pad and select Load Fuel in the loader's GUI. Once your vehicle is fueled, you are set!