Need help in Lego Indiana Jones please...?

Ok, i'm in level 5 of the Raiders of the Lost Arc story mode. Now i'm stuck with getting on top of a board walk. after i kill the enemies i end up getting marion on the crane and to a higher level which there is this RED BOX. Now what is this red box, i thought it would serve as extra weight for that "see-saw" like platform arrangement, but i can't seem to keep it on. do i use that mive weight to put on that platform or what. and how do you use that red box? thank you.