Can someone explain coupon codes?

I've searched for this in Rover Q&A and I'm still confused. So I purchased Rover business cards about a year ago and my 'coupon code' is on the back... is this still valid? And is this the same thing as a promo code? And if I give it to a first-time Rover using client, do they apply it when they finally confirm the booking or can they only apply it when first creating their account?