Hmm, it should only be a cross if you're trying to do an ILS landing. As I understand it, You are to maneuver the plane so that the velocity vector on the HUD is following the navigation line and it will bring you to the correct steerpoint as indicated on the HUD. You can double check your steering with the HSI on the front dash. You can also enable the auto pilot once you're on the correct course, which I always do if the waypoint is far.