bit rate tells you how much data per second is used to give you the content, mostly higher bit-rate is better quality music, lower bit-rate is mostly lesser quality music.

you should aim for a bitrate of 192kbit/s this is good quality, average filesize, most used bitrate out there

although i prefer 320kbit/s for freshly ripped music.
music ripped at 192kbit/s is good enough tho, and doesn't make a 4min mp3 10megs