Yep that's the basics of 2D parallax.
Do you know how to use playmaker? You should get the x and y position of the camera everyframe and then offset each background layer (id suggest breaking it into chuncks ie Hills, trees, car, whatever is in your game) and set the position of these with an offset to the camera position.
Lets say the camera has moved +10 in x .. the further away an object is, the less it would move! so the very background hills would be the camera position divided by lets say 5 so the position of the hills will be 2.
Understand?