If you download Karrot through a friend's invitation, you'll receive 1 carrot.

Collect 3 carrots to get a gift card. You can collect 2 more by inviting 2 more friends.

To invite friends, go to My Karrot > Invite friends > Share invitation

When your invited friend signs up AND verifies neighbourhood, both of you each receive a carrot.

Once you've collected all 3, go to My rewards to get your gift card!