Heightmap and movement with a heightmap

Well, I bought a map maker called Terraed and it creates a nice level for my game with little work, my question is this, how do I detect the height of a heightmap and create a camera movement that allows the player to move using the wsad key movement and mouselook, im really new to blitz 3d and I could use some help learning how to create a first person code (like that of half life) for a heightmap in blitz 3d. Can anyone help me create the code and then break down what part of the code does what?

Thank you,
Megaman Zero

look at the blitz3d tutorials by ray diaz (2 parts). it goes through some basics of a first person game using a heightmap.

look at the driver demo and the castle demo, both use terrains.