You swap referral codes with another person, and you sign up with each other's referral links so the other person gets extra points. This helps them achieve more VIP days on that site (which means their picture and a link to add them appears on the front page of the site.)
AngelicaAutopsy: "foshure bby! here's ma referral link: -insert link here-"
CathyCatastrophe: "heere's miine; -insert link here- kthxbye bbycakes!"