How do i backup and wipe my mac?

[AshleyP]

so i bought an extrenal hardrive.
ive backed up the whole thing.
now, can i wipe my whole mac and rest assured that all my files will be recoverable on the external hardrive?
if yes, how do i do that?
also, can i wipe everything but music?? and how?
thanks.
will chose best asnwer
uh, no, that didnt really help at all.
i think ive explained everything i need answered?
what would you like to know?