how can I make a FirstPersonHandler NOT moving up and down? It is possible to walk through the buttom and fly now, Of course both isn't wanted…
And how can I controll that the FirstPerson (or how ever you want to call it) can not go through walls?
For not going through the ceiling, adjust the heigtht of Your char on each update - call according to the terrein or whatever bottom Your char is standing on.
For wall avoidance You want to use collision detection between the wall objects and Your char or picking in the direction of movement but there is a thread somewhere around explainint this in more depth …