This web site has a growing number of sub-sites, each indicated by a picture or graphical icon arranged in the navigation column on the left.  If you hover your mouse over the icon, a popup message will describe the sub-site.

You can always identify which sub-site you are in by the title on the page and by matching the icon in the upper left corner to the icon in the navigation column.

Every sub-site serves a different purpose and is organized somewhat differently.  Most of them have a tabbed menu bar across the top to indicate the choices available within that area.   If you move your mouse across the tabs, the descriptive text underneath will explain what that option or choice does.