You will find that just about any well established online retailer will have an affiliate program for you to join.
Joining or signing up is free and can be direct with the seller or via an Affiliate Marketing Network.
How it works is that you place links to the seller’s products in the content of your blog, or by using banners on your website, or via social media channels. When your reader clicks those links and purchases a product from the seller – you make a commission!
Affiliate Networks like Rakuten, ShareAsale & Commission Junction represent thousands of sellers so you only need to join the network to gain access to a massive number of affiliate programs!