First of all we need to distinguish exactly what an affiliate is. And second why anyone would want to be an affiliate.
An affiliate is someone who sells products that have been produced by other people. These products could either be physical products or e-products. You will normally get a larger profit margin by selling e-products. With a physical product, (you or the vendor), have to physically wrap and post the product to the customer. With an e-product you can set it up to be sent automatically to the customer.
So an e-product only exists as a computer file unless someone wants to make a hard copy of it. As you are selling an e-product then it is normally downloaded by the customer to his own computer.
Many marketers produce e-products that they would like to be able to sell to as many people as possible. As they know other marketers will have different customer lists to their own. They invite others to sell their product on a commission only basis. What this means to you as an affiliate marketer is, you will advertise the product on the internet with a special code that is supplied to you by the vendor. For each sale that is made you will receive a percentage of the cost of the product. That percentage can vary between 4% for physical products to 75% and possibly more for the e-products. So affiliate marketing means you are getting paid a percentage of the sale price for introducing the customer to the vendor.
So how does this tie in with an SFI affiliate? You as an affiliate of SFI are going to send out advertising to encourage people to join SFI, TripleClicks and E commerce affiliates. As an affiliate of these programs you are going to get commission on TripleClicks sales. You are going to earn from those who you sign up in the programs. With the main SFI program you are going to gain VersaPoints when you get affiliates. You will also be getting commission on their sales. As you climb the SFI ladder so the number of levels you receive commission on increases.