In the world of the iTunes downloads, you computer has its own identity that is recognized by the download service. When you want to actually utilize the purchases from the iTunes Store your computer will have to be authorized to do so, which requires using your Apple ID and the accompanied password. Here is a look at how to authorize your computer for iTunes.
What most people do not understand is that you can authorize up to five computers with the same Apple ID, and this works across operating systems. Your device, however, does not count as one of these, so the iPhone or iPad is considered separate from this dynamic.
To set up your computer as one of those authorized for the iTunes Store go into iTunes and go to Store. Go down to Authorize Computer, and if you want to deauthorize one so as to authorize a new computer then you can select Deauthorize Computer.
When you select this a prompt will come up where you can enter in your Apple ID and the password. This will connect your iTunes account to your computer so that you can automatically download and interact with it, and then your content can be synced directly to your iPhone or iPad. It is good if your iPhone is also connected to iTunes with your Apple ID so that you have equal access to your iTunes Store purchases and so that you can initiate new downloads of music, videos, and apps from the App Store.
If you want to change the account associated with your computer you simple select Deauthorize Computer and then Authorize Computer with the new information since it is really just about logging on to your iTunes. It is important to note, however, that your iTunes account remaining logged in may give a chance for unregulated purchases to made on your account. Since iTunes is plugged directly in to your credit card information it will make financial deductions automatically after a certain amount of activity. The authorization will also work across the different areas of the iTunes Store including music, videos, apps, and even unpaid content like iTunes U and Podcasts.