Referrals
All sites offer some sort of referral plan. If you refer someone (a direct referral) and they use the site then you get paid some amount for their accumulated time. If that person refers someone who then joins and uses the site this new person is a direct referral for that person and an indirect referral for you. The various plans differ in how much you get paid for a direct referral and for each level of indirect referrals and on how many levels their referral program allows. While the referral rates are important in general the more levels a plan allows the better. For example, if you refer 3 people and each direct or indirect referral refers 3 people then a plan that goes 4 levels deep would give you 3 direct referrals and 117 indirect referrals. A 6 level plan would give you 3 direct referrals and 1089 indirect referrals. Note: You do not lose any income if you join a site as a referral from someone.

Spamming to get referrals: All sites have policies forbidding the use of any sort of spamming as a means of obtaining referrals. Some sites even list the names of users who have been suspended for spamming. Spamming to obtain referrals hurts everyone involved - don't do it! The same applies to any form of cheating.