In English, we use the Present Perfect (e.g. I have been) to express an action started in the past but that is still going on in the present.
Now look at these examples in French:
Notice that in French, to express the same kind of actions, we use depuis with Le Présent.
Depuis can mean both for + duration and since + date in this context.
Note that you can never use pour in that context.
See also the more advanced lesson : Using Le Passé Composé or Le Présent in negative sentences with ''depuis''