As soon as you try to do something that requires iTunes authorization, such as enable iTunes Match, a box will pop up asking you to do so. Just enter the Apple ID and password associated with the content you’re trying to access and Apple will automatically authorize iTunes on your PC or Mac. If you’d like to manually authorize iTunes, just go to the Store menu in the OS X menu bar and select Authorize This Computer. For Windows users, the lack of a menu bar means you’ll find this menu by clicking the small icon on the top-left of the iTunes window, illustrated in the following screenshot.