Mac iTunes Preferences.....which one?

My question is concerning importing songs...
under Import..... I have 5 choices:

AAC encoder
AIFF encoder
Apple Lossless encoder
MP3
WAV

can someone explain what they are (I know MP3 and WAV, btw) and when I
would use them? Any help would be appreciated. Actually any help with this bloody thing would be helpful. But this is the main thing for right now.

This is not the best place to ask. What about the support forums on the apple website? Many more people your side of the Atlantic using Macs.

thanks for the tip....apple support is designed for those who already know about macs....unlike some (or one) of us. It was worth a shot....someone suggested I try here. Anyway...I figured out which one worked best, even if I dont know what the letters mean. Thanks anyway.