Google Play Music is a multi-use app that both comes as a pre-installed music app on all Google-certified Android devices but can also be installed and updated from the Play Store on older devices. It works with music files that have been loaded on your phone manually, with streaming from your own collection uploaded to Google Play Music, with purchased music from the Play Store or even through a paid monthly subscription service to access even more music.
All Access is Google's subscription music service that lives within Google Play Music, giving users access to millions of songs for a flat monthly fee of $10. Those who subscribe to Google Play Music All Access have the ability to stream, download, create playlists and share tracks, regardless of whether they actually own them or are simply accessing them with their monthly subscription. All Access can be used across 10 devices tied to a single account, but playback is limited to one device at a time.
Google Play Music has evolved pretty dramatically since its first unveiling in mid-2011 when it came as an invite-only service, but is well-regarded as being a great all-in-one app choice for music lovers of all kinds.