The Oil Refinery is a machine that is used to process Crude Oil into usable Fuel. To make fuel, place an Oil Canister or external mod's fuel container (such as Buildcraft's Oil Bucket) into the top left slot. This will empty the container and fill a portion of the refinery's internal oil tank. Once the oil is filled into the refinery's oil tank, you can refine the oil if a valid power source is connected to the top side of the machine. This will convert the oil into fuel. You can then remove the fuel by placing the same type of container in the top right slot. You can now put the refined fuel into a Fuel Loader to fuel your Rocket or Moon Buggy. There are also fittings on the sides to allow pipes (from other mods like Buildcraft) to be connected. This allows oil to be pumped directly into the machine and the fuel out to a Fuel Loader. The black fitting is for the oil source and the yellow is the fuel output.
Tip: If Buildcraft is installed, a refinery from that mod is also included. Using the Galacticraft refinery is cheaper and requires less materials to produce. It should be noted that both rocket fuel and Buildcraft fuel can be used for fueling engines or rockets.