Pretty self explanatory, use the link below to find the deal and more details.
https://www.spotify.com/us/starbucksrewards/?referral=starbucksOffers only available to users who haven’t tried Spotify Premium. Supplies limited. Stars will be awarded during the Offer period or until 74,215 Offers have been redeemed. Once you redeem your Spotify Premium trial, Spotify will send an email to your registered email address in 3 days with your Star Code and instructions on how to retrieve your Stars.
Zrico.