Google is now offering a “Free for print subscribers” option for certain magazines in the Play Store. If you subscribe to certain magazines that offer this, you’ll see a login screen asking for your email address and password to your magazine’s online account. Once you see it, go ahead and select “subscribe”, then you will see an option called “free for print subscribers,” thus the magazine is available for free.
Note that this is only available on your Android phone or tablet and not in the Google Play web version on your computer.
source: Google Support