The FMS is what the pilot programs with the waypoints, the GPS tells the FMS where the waypoints are.
(had to look that up) I think I'm understanding a bit more what you're saying.
Is the FMS a software program in which you enter your waypoints, and the GPS targets it more precisely? (sorry if I'm sounding dense).
From your earlier post: it could be done in a few keystrokes on the FMS if he had inside knowledge. He wouldn't need knowledge of the other FMS functions. He might have been able to learn the keystrokes from Microsoft Flight Simulator.
Are you saying that shortcut key entries for the FMS would be the only thing necessary to know, not understanding the entire software program in order to make the plane lock on an area and have the altitude, etc., at the correct position/location?
And if my denseness is frustrating you, you don't have to explain. I don't want you to be pulling out your hair. : )