Book Essential help w music data retrieval

If I have backed up music, now itunes is empty. so if you retrieve it-- is still empty and in a folder in my documents. what in the world do i do? my kids are gonna freak out!

how do i get it to itunes?

and do i have to retrieve it EVERY TIME we want to use itunes?

And once I retrieve–does it have to be backed up again?

How did you move your Itunes to the drive?  Drag and drop or using a software?