Control Banebot motors using encoders

Hi everyone! I am noob to encoders and these arduino things. I want to know that what are the readings that an encoder gives me back when I use analogRead function to read the encoder outputs?

Are those values related to speed of Banebot?

I want to control 2 banebot motors using encoders so that they run on the same speed. I guess everyone knows that even after providing same pwm values to both motors, their practical speed varies. And I don't want a single degree difference in them.

If I can't use encoder, what should I do to control them? Thanks in advance.