this is a new topic and you should start a new thread for it, but before you do that try to find the solution by your own.
If you goto the Help section of the Editor, Command Reference, 3D section, you'll see a list of the command groups.
Goto the Terrain chapter and check out the Load Terrain sample.
Then for walking read the Collision commands descriptions. To make this a bit easier for you:
example:
t_player=1 ; define a collision type for all involved entities
t_ground=2
EntityType player,t_player
EntityType myterrain,t_ground
collisions t_player,t_ground,2,2 ; define collsion action that needs to be performed
while keydown(1)=0 ; main game loop
; some player controls here..
; (use your own code)
;apply gravity:
translateentity player,0,-.1,0
; apply collisions
Updateworld()
Renderworld()
Flip
wend
Please try the various examples that are part of the distro, you may save us and yourself a lot of time cause most basic questions are answered within them.