Can anyone help me understand audio quality???

I have many digital music files on my pc,i want the quality of the files to all be the same,but i really don't have much knowledge when it comes to sample rate,bit rate,mono or stereo.etc... I understand the higher the rate,the better the sound quality is,but i'm kool with cd quality (128 rate) What i want to know is what's the difference between Sample Rate and Bit Rate. Also the differ between mono and stereo. and which is the best when it comes to audio. Also between mp3 and wma, Which is the best when it comes to sound quality.I heard that mp3 is good for storing alot of songs on a disc,but wma sounds better since it isnt compressed.Im not sure.Plz Help!! Thanks.