Galactic Commander consists of nine phases which must be completed in sequence to pass the test and receive the accolade. You can practice on any level for as long as you need, but you must start from level one for the test.
Each level has an extra feature added to it (increased gravity pull, missiles, mothership, caverns, etc). If you successfully complete a level, you will automatically be moved on to the next.
If you go off the top of the screen, you should take your finger off the thrust key until you reappear. This may take a while if you are travelling fast.
A - Left, D - Right, RETURN - Thrust