There are a few pages on my site which have an in-page navigation menu. Normally this is only done for large pages, so that you don't have to scroll so much.
The in-page navigation menu is at the top-right of the main frame. It normally displays the text "In-page Navigation" or "Menu". It is fixed, meaning that is stays in the same place in the window, rather than the same place in the text, as you scroll through the page.
If you click the text "In-page Navigation", a pop-up menu appears in its place, showing all the chapters, sections and sub-sections of the page. Simply click any line of the pop-up menu to navigate/scroll to that part of the page. When you click in the navigation pop-up menu, it closes so that the text "In-page Navigation" or "Menu" is again displayed.
If your browser does not support the style "position: fixed" the in-page navigation menu will either not stay fixed, and will probably be shown at the end of the page, or more likely will not be displayed at all. Most browsers do support "position: fixed".
In Internet Explorer, there may be a short delay (300 ms) before the page is scrolled to the desired position. This is due to a bug in Internet Explorer (Version 7 & 8). For more information on this bug, see the section on known bugs.
There is also a bug, in that the in-page navigation menu does not reposition when you resize the browser window. You can force the menu to reposition by reloading the main frame (the frame containing the in-page navigation menu), by right-clicking and selecting "Reload Frame", or by reloading the entire window and navigating again to the page you were viewing.