This screenshot shows the Glossary and Concept window of Interbook. It is split in two to improve the readability but it is normally just one window.
You first click on a letter in the alphabet. Interbook then shows all the concepts starting with that letter. The colored balls indicate the status of these concepts: green for ready to be learned, red for not ready, and white for already learned.
When a concept is selected it is described briefly, together with a list of pages that contain knowledge of that concept, and also a list of topics for which the chosen concept is a prerequisite.
It is thus possible through the glossary to find out exactly what needs to be studied in order to learn a certain concept.