Affiliate marketing is a system by which you promote a product, brand, service or company through a Facebook page or groups to your contacts. Thousands of merchants including Amazon, Flipkart, VCommission, Shaadi.com and many other pay you to promote their products.
You can do so by joining affiliate marketing programs offered by these organizations and posting their content on your Facebook page. Every time an interested party looks up the advertisement or content you have posted and becomes its customer, you stand to make some money.