As, while, when.
Non ho capito le circostanze di utilizzo
As you said. (Refers to something you did,) As if. (Refers to something which is desired.)
While you wait. While you speak. While you are here. (Refers to a passage of time.)
When did you arrive? When do you want to eat? When do you sleep? I sleep when I am tired. (Refers to a specific context.)
Hopefully this helps a little.