A DWiki is made up of a bunch of pages in a directory hierarchy. (This is unlike a traditional wiki, which has a more or less flat namespace with no directories, subdirectories, etc.)
Every DWiki page has 'breadcrumbs' up at the top of the page that show where you are in the DWiki's directory hierarchy and give you links to everything above the page. For this page, that says that you are in the help subdirectory of this DWiki's root.
If you go to a directory it will generally tell you what pages and subdirectories are inside it. Some pages, like the DWiki's starting page, will usually tell you what subdirectories are in their directory, so you can jump directly to something that seems interesting.
(Some directories show different views of their contents than just plain lists of what pages and subdirectories they have. If you hit a directory like this, you can use the Page Tools at the bottom of the page to ask to 'See As Normal' to get a simple list.)
By convention, in Category are some automatic indexes of pages that mark themselves as being in various categories.
Note: because most of these pages list some variety of everything in the DWiki, they may get very long.
If searching is enabled and available to you (it depends on the DWiki's configuration), the bottom of every page will have a 'Search' box where you can enter a word.
Unfortunately DWiki searching is kind of simplistic right now; you have to search for a word, and you have to get the capitalization right. (With cleverness you can search for a phrase.)