I cant hear anything in this program.

I just want to know why cant i hear anythting.

Good question, given how little information you have provided I think I am going to blame it on the flying spaghetti monster.

So you might want to start by clarifying what is happening or not happening. Whether you are able to start Jack, if other programs are giving audio, what OS you have, what interface you have, what your current Jack settings are, etc.