What it is: Google Play Music is a streaming music service from Google that lets you to listen to music with an automatic sync between all of your mobile devices and computers.
What it does: It stores all of your music in the Google Music cloud, and this is what allows for the automatic sync.
You get free storage of up to 20,000 songs, and it also includes movies, TV shows, apps, books, magazines, and games as well as an online store.
When you buy a song from Google Play, you can recommend and share it with friends on the Google+ social network, and they'll get one full play of the entire song. Google Music iPhone and iPad people can't buy music here, it's an Android App only, but iPhone and iPad people can still use the Google Music Beta for cloud-based storage and streaming of their music. Google has just added a scan and match feature, which means it will take less time to make your library available in the cloud. Google will scan your music library and match songs in your library with pre-existing versions of the same song in the cloud, with good sound quality. This allows for an improvement on sound quality for most users, while also cutting the upload time for your library down substantially.