Comments are important in the outside world of web design. We don't use them so much in our department, because everything is fairly straight forward. You are being showed them, however, because they are being used to explain some things about the video player we use in pages that have videos.
Comments are text that explain something that don't show up in the front end of the web page, much like the tags. They Generally go outside of the tags, so as to not throw off the flow, but they can go inside the paragraph if needed. If you look at the code at the end of this paragraph, you will see an example.
VIDEOS!