You need to create a bone in the place of where you want the player to sit and name the bone 'mount0', for passengers, you need to create bones named 'mount1', 'mount2', 'mount3', etc
For wheels, you need to make bones where you want the wheels to be and name each of the bones 'hub0' (front left wheel), 'hub1' (front right wheel), 'hub2' (back left wheel), and 'hub3' (back right wheel)
You'll also need collision mesh, which you can make by just making a box, or any kind of simplistic mesh, and fitting it to the size of your vehicle and naming it 'collision-1'