Sunandpaper

Hi all, I am a new GMRS user in Pittsburgh PA. I would love to test my Midland MTX400 but don't really know how to hit a repeater with it. I understand that I need to be on the repeater channel and dial in the correct squelch (please excuse my ignorance of technical terms.) But how do I get anyone to give me the right DCS code? I've requested 2 repeaters near me but haven't heard back. I would love to be able to just see if I can hit anything from my location but haven't had any luck at all so far. All I've been able to pick up is a couple low power transmissions (FRS?) Any and all advice / comments would be greatly appreciated!