One of the oldest forms of Marketing
Affiliate marketing is one of the oldest forms of marketing wherein you refer someone to any online product and when that person buys the product based on your recommendation, you receive a commission.
The most common question I hear is related to how companies track the record of who is sending the traffic and making the sales. The simple answer is with a tracking URL (a unique link given to you by the affiliate company or product company).
This URL is used to keep track of all the traffic and sales you are making via your website or other promotional techniques. Many old-fashioned affiliate programs allow a buyer to add the email or referral details in an effort to account for affiliate sales, but this is certainly not the best way to track progress.