codes and brakes

I have been seeing you all talk about codes and using a device to see them when check engine light illuminates. Where do I get this device and how spendy is it?

Also, when I apply brake, I hear a noise somewhat like a little fart. Not really big, just a little tiny frump. Brakes are, to me, a bit weak. I own a 97 LT with 83k miles. Wonder maybe if there is air in my lines. Any thoughts? Thanks everyone.