Earning by comments will require you to have your own Blogs and Websites. You will then share these dedicated domains (Owned by You) in the comment window. If an option to add your URL or website is not available, then you do not include links. You contact the site support first and get permission to share your URL. Oh, and NEVER share affiliate links in comments.
For example, let’s say you signed up to become an Amazon Associate so you can make money as an affiliate of Amazon. You then create a gardening video showing people how to plant a small tree. Find the exact shovel you are using in the video, on Amazon, get your affiliate link and put it in the description of your video so people who are interested can buy the same shovel on Amazon. For every person that buys the shovel, you earn a commission.