Have a read here:
There are several reasons for having an Apple ID - for example if you wish to use the "Find my iPhone (iPad) " feature on someone else's computer.
Basically, I find it best to use your usual e Mail as the "Apple ID" and to have a secure password in the password box. I do not have an open account with Apple with my credit card - I use those £15 or £20 vouchers. In iTunes, when you log in with the correct ID and password, and go to the "store" option, it tells you the remaining credit. I would use the same ID and password on the laptop and the iPad. I have more than one ID as a granddaughter also uses my PC but for now I would stick to one. If you live near an Apple store they will help set it up. If not, telephone the nearest one and they will put you through to tech support. Have your serial no ready - they are helpful.