The all-access subscription is a music service and comes with YouTube Red so that you avoid ads on Youtube. It also lets you play YouTube videos in the background or while your phone is locked on android devices (support should be coming for iOS).

You can also put Google Play credit towards it. I had $5.65 I had earned from Google Rewards (highly recommend this for android users) I put it towards my subscription. I got it for $24.32 for 6 months.
If you're on TMobile music streaming on Google Play music will not count against your data cap.

Simply send yourself the gift.
https://play.google.com/music/gift?#