The Oxygen Compressor is a machine added by Galacticraft. Its main purpose is to fill Oxygen Tanks so surviving in space is possible.This is necessary when staying in a Space Station or on another planet for extended periods of time.
To fill an Oxygen Compressor you must first craft one (see below). Once crafted, you must connect it to a supply of oxygen which can be produced by an Oxygen Collector , and distributed by Oxygen Pipes to the side with the grey circle. Once supplied with Oxygen, a power source must be connected to the side with the blue square. Now just put an Oxygen Tank in the output slot on the bottom right to fill the tank.