IF you want to use collision on a map, Intersect Object is your friend.
h# = Intersect Object(levelobject, x,-100,z, x,100,z) - 100
Basically, it makes an invisible line and returns a 0 if the line doesn't intersect your object, and if it does, it returns the distance from the first point to the intersection.
In the example I gave, the x and z are the coordinates of your player object, and it makes a vertical line from -100 to 100, and figures out how high up it goes before touching your level. To find the height of your terrain, we have to subtract 100 afterward because we started at -100 and not at 0. So now, you can just position your player like this:
Position object playerob, x,h#,z
To do collision with walls, you would have to use horizontal lines instead, but this gets more confusing. Do some research on intersect object.