To navigate through this CD you are supposed to use the navigation buttons of your browser.
On most of the pages there's also an button available, which leads you to the page you came from. Sometimes one picture or table or text is linked to from different texts and then the button goes back to the page in the course where the picture or table or text was used for the first time.
A button is used when there are different texts or pictures which are related to each other. By clicking on you arrive in the next part of the text.