The latest version of iTunes is now available for download and with it comes Apple's long-awaited music streaming service. The update also includes support for iOS 7 devices and seeing as how the new mobile OS just went live, you'll want to pick up version 11.1 of iTunes if you plan to sync your device(s) with your computer.
iTunes Radio is perhaps most like Pandora in that it offers custom "radio stations" based on artists, song or genres. There are 250 preset stations available from the get-go should you not want to fool with creating a custom station right away.
iTunes Radio can be enjoyed ad-free for those that have subscribed to iTunes Match at $24.99 per year. That's a good bit cheaper than the $8-10 per month that other services charge but there are a few notable features missing as of writing (offline mode). Of course, iTunes Radio is also available free of charge but you can expect a fairly regular dose of audio and visual ads mixed into the experience.
In related news, iOS 7 is now available for download for compatible iPhones, iPads and iPod touches. This free update has been thoroughly picked through by the media ever since it was shown off at WWDC back in June so I'll spare you the details. In summary, the software is described as having a much more flat design with an emphasis on text and colors - an anti-skeuomorphic UI, if you will.