What would an AMP do to my speakers?

I have an entry level surround sound systems with a Harman & Karman 153 receiver - JBL in wall speakers and a JBL center channel with a PB10 sub.

The question is what would an AMP do to my home theater ? Would it increase the sound of my speakers ? How do you connect one ? I assume you hook it up to your receiver and your speakers will hook up to the amp.
No clue - I'm just guessing.


Thanks