Okay let me explain. a bit rate like somebody else said is how much information is encoded on that file highering or lowering quality depending on what bit rate you encode to. I choose a 192 bit rate with my songs because to me even though it's not, it's clear enough to be cd quality. Alot of people choose 128 as their bit rate because you can fill your music device with more songs being it's a smaller file taking up less space, but I'm not to fond of that. I think anything below 128 or higher than 192 is just a waste of space(192+) or too fuzzy to listen too(12
. As for what formats. Either mp3 or AAC is good. I choose mp3 over AAC because mp3 is more appliable to programs and tools, but AAC is known for better quality.