I just purchased World of Warcraft for my pc. I have no idea what the other three dics are for that came in the box. There are not any key codes on the three discs and nothing happens when I put them in my laptop.
If you purchased the game new, the disks should have come in sleeves that look like this:
The white sticker has the CD key that you would use to activate your account. (Here it is blurred/greyed out for obvious reasons). If you bought the game and it doesn't have these sleeves (or something similar with a CD key) then you probably got a copy or something that's not legitimate. You could always try to call Battle.Net support for help too, which I would recommend heavily.
Side note: You don't actually have to purchase the physical game disks. You can go to the Battle.Net store and purchase a authorization key that will let you create an account, download and install the game and play.