How to use UAV:
Activate the UAV Terminal
Then when you are in the UAV hit "m" to bring up the map
Click anywhere on the map, UAV will automatically move to that location, then begin a circular holding pattern around where you clicked
Press "m" again an use the UAV's camera to find the enemy!
Makes sure to toggle FLIR (thermal imaging) on with "n", so people and vehicles become easily visible
Note: There is no way to directly control the UAV, only give it general directions.
As for your UAV crashing problem, well that's just a usual occurrence in ArmA, something we have to come to terms with before we can truly enjoy the game :p