Using a mixer


Hey, I have a behringer xenyx 1622fx mixer and the manual for this doesn't quite educate me enough and I haven't found really anything really definitive on how to use this mixer. I would just like to know what every part of it can be used for and how to use them.
Here are all the things unknown to me: main/sub/control room outputs, aux sends, stereo aux returns, the dB scale on the faders(why does it have negative numbers and then has the infinity symbol at the bottom?) fx footswitch, and there is a button that says 'pre' and goes with the red aux knob.
Also, I have two vocal mics that have xlr to 1/4 in. cables. If I bought cables that just went to xlr, would that yield a better quality sound?

This is my first mixer and I have a small understanding of how to use it and I have been figuring out a lot things by experimenting, but there's a lot of stuff on this(perhaps more than I could/will use) and it's overwhelming.