Comments is something you probably know from blogs: Right below an article (or post) there is a form that allows you to comment on this specific article. Comments are usually published instantly so other blog readers (as well as the blog author) can read them and reply.
Reading and writing comments takes place in the detail view. Below the information itself you can see existing comments as well as a form for new comments.
You can see the name and the photo (if available) of the author of each comment. For your own comments you have the possibility to edit or even send the comment to the trash, and you can link the comment to another object (see Linking objects).
As soon as you publish a comment you are automatically subscribed to this object. This means that you will get notifications about additional comments.