This deal expires in a week.
They are giving $15 credit toward a purchase at Target through Google Express.
To get the deal, you need ONE of these: A Google Home or Google Home Mini voice-operated speaker, or The Google Assistant app for Apple or for Android. Link the Google Assistant to your Google account. To confirm your account is linked, say "Hey, Google, what's my name?" If it answers correctly, your account is successfully linked.
To add $15 credit at Target, say "Hey, Google. Spring into Target" (Or, this can be typed into the Google Assistant app)
Google Assistant will tell you the deal has been added to your Google Express account. Go to The Target Store at Google Express and shop for at least $15 worth of stuff.
Note that shipping costs about $5, or free with a $35+ order, so: Order $15 of stuff for $5 shipped, or Order $35 of stuff for $20 shipped. The $15 credit must be used by April 21 (this Saturday).
For example, buy a Google Chromecast for $20 shipped with the $15 credit.