There are thousands of Affiliate marketing sites online, All these sites offer different affiliate marketing networks which all depend on the mother company. There are two forms of Affiliate programs one involves referring someone to the any platform of Affiliate marketing  then anything they get to purchase you get commission out of it, an in the case they refer someone else that other person commissions on there purchase are not going to be added to your income but the income of the person you referred only.
The other form of referral is where if you referred someone they become your permanent referral  anything they purchase for life you get a commission and one of your referral refers someone else under them you still make additional commission from them but calculated based on different actions unlike your first referral. Its the most preferred since you can make a lot of money if you only refer a few active referrals. Some of these sites include;
   Strong Future International .
This offers you many ways  to make your money simply by registering a free account, then you will be given lessons on how the system works.It also has many different ways of making money from sponsoring, generating sales and other additional income forms.
   Click Bank.
In this Affiliate program you it mainly focuses on a wide range of digital products here you will be required to search any product that you are able to promote comfortably then you are provided with affiliate link to the product and you can begin promoting immediately to make you some money.
Another Affiliate marketing that  provides its users with additional ways of making on different ways of making money and it also provides you with advertising services since most Affiliate marketing involves mostly advertising which is basically driving traffic to your Affiliate links to make good chances of converting easily.
  Amazon Associates
This Affiliate program is preferred by  many because of its wide range in products. With many products its like walking into a mall,if you referred someone to a mall the anything they buy in the mall gets you a commission and not a specific product you might have referred someone to buy.
  Commission Junction
Here with one account you are provided with access to other Affiliate programs, Many companies offer different forms of marketing you can go through many of Affiliate program on this site and find a suitable company based on your niche of expertise and start making some income online.