Google is currently running a special offer for its subscription Google Play Music service. When you sign up for the service as a new subscriber, you'll be able to get your first four months for free, paying $9.99 after the trial is over.
All you need to do is head over to Google Play and sign up for the service. Note that when you sign up for a Google Play Music subscription, you'll also get access to YouTube Red, which offers all existing YouTube content, as well as exclusive videos, without ads.
The offer is only available this weekend to celebrate the Fourth of July, so you'll want to act fast to get that extended trial period.