Bonjour Varsha !
These are two different "since" :)
- "Puisque" means "since" in the sense of because, for, as :
Since you don't want to help me, I'm going to deal with it myself.
- "Depuis" is more of a temporal "since", i.e. from that moment in time :
I've known you since 1994.
I hope that's helpful!
Bonne journée !