Here's a quick example based on LearningProgram004, Joyce.  Basically, I added a second UFO to the program, move them both, and when they collide I make one of them disappear and the other one grow in size.It sounds like a very fun game - glad to help more as you work on it!

Here you go, Wolf - the zip file linked above should have a running version of your program in it.  I'll also paste it below.  The main thing you needed was a "while" loop which keeps running, watching for keys over and over again, and moving the tanker when a key has been pressed.  Try it out, then ask some questions, ...