Can anyone tell me how to make the plane fly automatically using the flight plan I made in Flight Planner? This is for MS Flight Simulator 2000. PLEASE HELP ME! I tried everything!

It will only follow the route. You still have to control speed, climb, descent, etc. Once you've created and loaded the flight plan, you have to select "GPS" on the Nav/GPS switch. There is a selection for that in the overhead menu (under nav radios, if I remember correctly) , or a switch somewhere on the panel. Then you have to select "NAV" mode on the autopilot.