If you’re a blogger, start by going through your analytics and finding your most popular posts. In Google Analytics (GA) you can find these pages by going to your GA Dashboard > Behavior > Site Content > All Pages. Examine the ones at the top of the list that bring in the most traffic. Are there any affiliate products or services you can naturally include in them?
Some merchants run their own (in-house) affiliate programs using dedicated software, while others use third-party intermediaries to track traffic or sales that are referred from affiliates. There are two different types of affiliate management methods used by merchants: standalone software or hosted services, typically called affiliate networks. Payouts to affiliates or publishers can be made by the networks on behalf of the merchant, by the network, consolidated across all merchants where the publisher has a relationship with and earned commissions or directly by the merchant itself.
Before jumping into starting an affiliate marketing business, learn all that's involved in making it a success. More importantly, if you decide to pursue an affiliate marketing business, or want to add affiliate marketing to an existing business, understand that it's not fast, automatic, nor without effort. Like all home businesses, you need a plan and daily involvement to make money with an online affiliate marketing.
Find a profitable niche. Starting with your interests, write down as many niche ideas as you can. Think about topics people might search online. Ideas include passions (like surfing or body building), fears (like spiders or speaking in front of crowds) and problems (like getting out of debt). Do keyword research to see it others are interested in the topic. Find out if a domain name is available that matches the keyword 100 percent. 
A niche affiliate site often presents like an eCommerce store. To get started with an affiliate site, choose your niche then display products with pictures, descriptions, and prices, just as you would on an online store. However, when visitors click the ‘buy’ button, they will be taken directly to Amazon, to make the purchase. You then make an affiliate fee for sending the traffic to Amazon, but have none of the packaging hassle, or initial financial output creating or buying the products.
Win-win-win. The advertiser wins because they only pay when a purchase is made (as opposed to the shotgun approach of paying to advertise to the masses and waiting for a small percentage to actually buy). The affiliate wins because they make money while providing helpful advice. The customer wins because they get a trusted recommendation for something they might not otherwise have known about.