If you know anything well, a place, how to fix something, how to make something, how to do something, you can write a guide for it. You can sell your guide as an e-book, offer it as a download for a fee on your site or reach out to bloggers with similar content and ask if they will offer it as a paid download on their website (for a price of course).
The term affiliate marketing has taken a bad rap over the years, primarily because people are abusing just how easy this is to do. Internet marketers are finding products they don’t even use because they come with a sweet commission, and are spamming everyone until they either buy, or unsubscribe. This is also known as the dark side of affiliate marketing. https://charliepage.com/wp-content/uploads/2017/10/How-To-Create-True-Passive-Income-1.png
Creating passive income is the key to retiring, especially retiring early. If you want to retire early with the stock market you will have to save a huge amount of money, because that money has to last so long and retirement calculators depend on you using your investment to fund your life. With passive income you will have income coming in as long as you own the investment, without every eating away at the principle invested. Creating passive income may take more work than investing in the stock market, but I think it is well worth the extra effort!