If you have Resistance, the easiest way to do what you want is to use the
onMapSingleClick command. In your init.sqs script, put the following code:
onMapSingleClick {car1 doMove _pos}
Whereever the player single clicks on the map, car1 will move there. Obviously, rename
car1 to whatever your car is really called. Good luck!
Edit: Note that this method does not require the use of markers. It's far simpler. If you want to use markers in addition, you can create a script to do more complicated things.