Amazon’s affiliate program is the most popular of them all. I don’t participate myself (yet) but the majority of affiliate marketers I know use Amazon because… it’s Amazon. You can review products you have used or write tutorials (eg. how to connect computer to TV) and drop an affiliate link to an HDMI cable… just a couple examples. You may want to build relationships with the manufacturers so you can get products before they’re released – giving you time to create a review before the product is launched and capture sales during peak buying times.
I will give you a very simple example. Let’s say you build up an audience of 50,000 readers and out of that 50k you have about 1% that trust you (1% of people that trust you online is actually very huge), so that equates to 500 readers. Out of that 500 readers you will have about 10% that will buy your eBook and other affiliate products, so 50 people total. So, if you are selling your eBook for $10, you will make $500. Of course it doesn’t stop there, those people that buy the eBook and like it will most likely recommend it, and you will have a snowball effect where more people keep buying your book and other affiliate products. This is just a rough example that shows you some realistic numbers. Do not ever think that if you build up a huge number of readers that they will all trust you and buy the products that you promote; if it was that easy everyone would be a millionaire by now.