The mission scenario descriptions were circulating both as a text file and in the hint section of a computer magazine we had, but I didn't get either for a long time. "Zulu alert" mode lets you take as many enemies off the sky as you can, with infinite ammo.

Edit: I now remember that the first training mission is something like "shoot two target practice boards in sector E5". You have to be very meticulous to find those just by flying around!