Early in the game, you will need to obtain a data cartridge from the Arcada's library. You will know which cart you need when the time comes, but to actually GET it, you must enter the right code. Look up the cart name here and enter the corresponding code at the library console to retrieve it.
Later in the game, you will be in command of a small starship. To continue, you must tell your 'pilot' where to go, again using a special code. Assuming you know which sector of space you're supposed to be heading towards (learned via an in-game puzzle), look it up here and enter the corresponding code.
WARNING: If you enter a code for any sector OTHER than the one you're supposed to go to, or if you don't enter a code at all (by pressing the OFF button), you will be killed in-game. Save before attempting.