How do I apply a promo code?

What payment methods do you accept? How do reward points work? Do I get a discount for referring friends? How do I get a receipt? How long do refunds take? Is my credit card information secure? How do gift cards work? How do I purchase a gift card? How do I redeem a gift card? Do gift cards expire? Can I use a gift card with other payment methods? Can I check my gift card balance? Can I get a refund on a gift card? I didn't receive my gift card email