Okay. If you want to learn more about CONTROL CAMERA USING ARROWKEYS, you should check the help files (press F1 in the editor).
Here's the other code you posted, explained:
rem Control camera over terrain
`This code needs some preparation to work properly.
`First, you need to make an advanced terrain object
`Use MAKE OBJECT TERRAIN and the other advanced terrain commands.
`This command allows the user to easily move forward and backward with the UP/DOWN keys.
`And turn left and right with the LEFT/RIGHT keys.
control camera using arrowkeys 0,3.6,3.6
`This stores the camera's (player's) position so we don't have to keep typing CAMERA POSITION X(0)
cx#=camera position x(0)
cz#=camera position z(0)
`These stop the user from going off the edge of the map
`If the player's position is outside the map, it sets it back inside.
if cx#<0.0 then cx#=0
if cx#>size# then cx#=size#
if cz#<0.0 then cz#=0
if cz#>size# then cz#=size#
`Finally, this gets the height of the advanced terrain object,
`and positions the camera (the player) at the right position.
position camera cx#,get terrain height(TerrainNumber,cx#,cz#)+24,cz#
Note the code boxes. Whenever you post code, you should put it in a code box by pressing the "Code" button so it's easier to seperate it from the rest of your post.