You can access an Apple Music subscription in a number of ways. On an iPhone, iPad, Mac, or Apple Watch, you would use the Music app.
Apple Music - Apple
Get started with Music on iPhone - Apple Support
Note that you only have access to the music for as long as you are a subscriber. While you can download offline listening copies (if you have Sync Library turned on), to let you play music when you do not have a connection to the Internet, those are only for convenience.
They will be deleted, or stop working, if you cancel your subscription.
If you decide not to continue the subscription, as a paid subscription, be sure to cancel at least a full day before the end of the trial. Otherwise it may automatically convert Into a paid subscription.