Following are few tips that might help you clear some doubts in using Google Music:
1. It can automatically back up iTunes and most other music flies. When you set up the service, you can tell it to upload your iTunes library, your Windows Media Player library, or any file folders you designate. The service supports more file types than competitors iTunes and Amazon Cloud Player. This includes not just the MP3 and AAC formats those support, but also WMA, OGG, and FLAC. The latter are saved as 320 Kbps, even if your originals are of higher quality.
2. It's two separate sites. Google Music is the player and library, but you buy music on the Android Market site—whether or not you ever use any Android device. From the Google Music site, you can also download an app, Music Manager, that scans your PC or Mac for music files and upload it to your cloud-based music locker. The Android Market is where you browse, preview, and purchase new music, which then appears on your Google Music pages or in your Android Music app.
3. You can't download songs to another computer unless you bought them on Google Music. iTunes Match and Amazon Cloud Player let you download stored music to any computer or compatible mobile device.
4. Some Android devices fully support it, some don't. There is, of course, an Android app, but that hasn't yet been updated with all the new features, and some phones and tablets still don't see music in the Android Market app yet. The whole point of Google Music is to finally give Android mobile users an equivalent to the iTunes services enjoyed by iPhone and iPad users. Google states that this will be updated within days, but it's unclear which phones and tablets' Android versions will be updated on what schedule. Some Android phones and plans, starting with T-Mobile, will even let you pay for music through your phone bill.
5. There's no official iPhone app, but music.google.com works on iOS devices. The Google Music site is even formatted well for iPhone screens. You can listen to any music in your Google Music cloud locker and even buy music from the separate Android Store, but you can't back up music on the iOS device to Google Music. Nor can you download music bought in the Android Music store to the iPhone directly (see #1 for how to do it indirectly).
6. There's tons of free music. But you need to give Google your credit card information even for the free stuff. This could be a concern to those who worry about Google profiling them.
7. You can only share purchased songs to Google+. If you do so, anyone following your Google+ profile will be able to stream the full song once. A Buy button is prominently displayed. Songs you uploaded but didn't buy at the Android Market don't get this treatment.