To use Apple services you need to start with an Apple ID. Your Apple ID is based on an email address you would like to associate with your account. Your Apple ID is your gateway to adding all kinds of content to your iPad, including Music, Apps, Movies, and Books. When you set-up your Apple ID you have the option to also use the same ID for your iCloud services account. However, this isn’t a requirement. You can also choose to set-up one Apple ID for for iCloud services, and a separate account for your iTunes, App Store, and iBook Store purchases.
Confused yet? Apple recommends creating one ID for both services to eliminate some of the confusion. They caution that using multiple Apple IDs might be confusing and might cause issues with accessing purchased content or using some services. However, in the event that you still want to keep your services separate, he is a quick and dirty how-to.
How to change your Apple ID
Whether you want to change an Apple ID for your iCloud services or your iTunes account, the process is the same. The first step is to sign out of the account you are already signed into. You can enter your Apple ID on your iPad when you are setting it up for first time, and it will be used for all your Store purchases and iCloud. If you skipped this step, or want to change it any time thereafter
Settings –> iCloud –> Select your Apple ID and sign in to change your iCloud ID. To change your Apple ID for iTunes and other Apple Stores, Settings–> iTunes & App Store–> and sign in.