Apple Music comes with a free three-month trial which, according to some people who haven't been paying proper attention, is something Taylor Swift arranged with Apple. Thanks Taylor. Three months is a good amount of time to try out the service, but Apple automatically signs you up for an auto-renewal payment option. So when the trial comes to an end, you’ll start paying for the service, regardless of whether you're still using it or not.
If you’d rather decide for yourself when (or not) to join up as a paying member, rather than being forced into it, it’s easy enough to turn off the auto renewal, although the process is far from obvious.
All you have to do is go into Settings > iTunes & App Store. Tap your Apple ID, select "View Apple ID" and enter your password.
Tap "Manage" under the Subscriptions option, and toggle off "Automatic Renewal" for Apple Music.
If you're on a PC or Mac, you can disable the Apple Music subscription through iTunes. Click the "Account" icon at the top, and select "Account info". Log in to your account, and click "Manage" next to Subscriptions under Settings. Click "Off" next to Automatic Renewal.
You can now enjoy Apple Music without worrying that you’ll be charged for it once the free trial comes to an end.