The Concept pane displays conceptual information about the document that is selected in the outline. If a topic is selected, and there is no concept attached to it, the Introduction frame appears instead. 

The conceptual information can be text, graphics, or a combination of the two. Concepts may also launch external content, such as a document, a presentation, web page, or a file. Depending on how the external content is linked, you may need to click a hyperlink to launch the content or it may launch automatically when you select the outline item.