The Play Newsstand is the Google's way to read your favorite magazines and newspaper on your Android device. Some of these magazines, which can be found both on the Play Store and the Play Newsstand, offer a free trial, so you can get unlimited access to that content for a limited time and after that your subscription will be started and you will be automatically charged.
To manage subscriptions and cancel free trails for magazines (before it's too late), do as follows on your Android device:
1. Open the Google Play Newsstand on your Android device (This is a default Android application on your device)
2. Tap the 3line icon on the top left, and then touch the My library option
3. Tap the Magazines tab
4. Now the list of magazines you are already subscribed to, is shown
5. Tap the 3dot icon on the top right and tap the Manage subscription option
6. You are redirected to a Google webpage, where your current Newsstand subscriptions listed (You may be asked to enter your Google's password)
7. Tap the Cancel button for each magazine you want to cancel the trail (or the paid subscription) and confirm the process.