If you referred someone and you've been awarded referral credits, they will automatically be applied to your next purchases until it reaches $0. Before confirming the order, you’ll be able to see the credits used in the payment section.
If you were referred, and have already made your first purchase (minimum $10 in one transaction), then congrats! You did it! Your $5 credit was already applied to your first purchase. Easy peasy lemon squeezy!