you have to use object collision commands to tell the object to stop when it hits any objects that are walls, ascend if you are hitting a stair and the bit in front of you is just a small amount higher than you are etc, you have to instruct the game what to do in each instance, stop the player, lift them up, make them fall etc, save your old player positions before you try to update and then if the player object hits something just move back to the position before any collision occured, so if you keep trying to got through something you stop still, then theres sliding collision, but that means more work and useing intersect object (if you stick to the inbuilt collision and have pro).
Mentor.
PC1: P4 3ghz, 1gig mem, 3x160gig hd`s, Radeon 9800pro w cooler (3rd gfx card), 6 way speakers.
PC2: AMD 2ghz, 512mb ram, FX5200 ultra, 16 bit SB.
Mini ATX cases suck.