i downloaded the fps tutorials, but i dont know how to hide the models of them.
like when your not shooting to hide the gun
Any GameObject can be turned off.
All you need to do is to find the GameObject you want to make active(show)/inactive(hide)
http://unity3d.com/support/documentation/ScriptReference/GameObject-active.html
If it’s only to hide the object, I would use the following:
gameObject.renderer.enabled = false;