Show GuiBox on camera

[G.G]

I am new of Unity, and i have try to make a simple viewer of gameobject.

At the object i have added a simple muvement script with 3 rotation (itween with rotate by push key - getKey).
At camera i have added a script with rotate around to vector with game.object and itween moveby.
http://giandgi.altervista.org/anello/web.html

Now i have create on the camera a gui box with the letters of the muvement (W-A-S-D and Y-U, H-J, N-M).

Assign at “Main Camera” a script with void OnGui ()… guibox(new Rect(),“W”) has no error, but i do not see the box.
What is my mistake?

[G.G]

solution found: make an gameobject empty and add the script with void OnGui and button… with this it is visible on main camera with script void Update (tween + rotate around).

Ok, i need to found a good explication of void ^_^‘’