Car falling down and down in the terrain??

hi I am a beginner in unity and making a car game for pc in a hilly area.I have download a car prefab and move it in view and i also assigned a first person controller to the view and then drag that controller to the car to move it.But when i hit play it starts falling down in the terrain and keep moving.how should i move my car in the scene instead of falling.should i use raycast or not assign FPS controler to the car or what?help plz!!