I know that you are suppose to state intentions right away. Like, flirt with her and let her know that you are into her.

I understand this completely. But, there is one thing I'm not really grasping. How far is stating your intentions? I mean, when is it appropriate to tell her that you're just here to bang, friends with benefits, etc? I get the idea of showing that you find her attractive and all. But, if someone can explain. That would be great!