Ok the main object in your game will have an (x,y,z) position and an angle. To put the camera behind it, you need to use the newxvalue and newzvalue commands. These work by: you put in an angle and a distance and it will move an object (or the camera) that far in that direction. To get 3rd person you need to put the camera directly behind the object. Note:- all this assumes you are working with 2 dimensional camera movement, i.e. you'll only ever have to rotate it around the y-axis, the y position is generally fixed in relation to the object, like in most car racing games. 3 dimensional camera movement, for example in space fighter games, is much harder. I haven't quite managed to perfect it myself.
camerax#=newxvalue(x#,(an#+180),dist#)
cameraz#=newzvalue(z#,(an#+180),dist#)
cameray#=y#+height#
position camera camerax#,cameray#,cameraz#
point camera x#,y#,z#
Where camerax#, cameray# and cameraz# are the camera coordinates, x#, y# and z# are the object coordinates, an# is the y-axis angle of the object, dist# is the distance you want the camera from the object, and height# is the height above the object that you want the camera to be. The angle used is (an#+180) because we want the camera to be 180 degrees around the object, which is behind it.
Hope you understand that.