Comments are explanations of individual passages in the Bible. They typically take the form of an encyclopedia entry or devotion and are designed to help you get more involved with the Bible text.
You can find them in the sidebar of the text view. It lists the different comments. The number in brackets indicates the number of matching entries to the Bible text.
If you click on a comment, the comment view opens showing all entries of a comment to the Bible text. The selection menu at the beginning allows you to switch between the different comments.