Long story short I imported a FPSC map to Dark GDK, I didn't know how to make the character collide with the map's objects a lone, so I added a square on every part of the game for the character to collide with(about 50 :S).
I know there might have been a much MUCH better way, but I needed something to be done at a certain time as fast as possible, now all I need is for the character to use the stairs, so for the character to collide with the stairs I did :
dbMakeObjectBox(192,600,150,10);
dbPositionObject(192,2100,530,-1465);
dbRotateObject(192,40,0,0);
Then put the object on top of the stairs.
But I don't know how to code the idea, of him "when colliding with stairs from down to go up and from up to go down"