Affiliate programs are ways for you to make money by directing people to some other companies products and/or services. Typically you don't have to sell anything. Instead these programs are made for you to link to their web site. Your web site visitors would then sign up for their services or buy their goods.
Usually the Best Affiliates will provide you with a finders fee or a percentage of the transaction, or even a payment for every user sent or that clicked through. This site is dedicated to telling you about the safest and most well known programs, how to sign up and what to expect.