Actually the main window may look like anything because its appearance is completely configurable via template themes. This page describes the default template that comes with DokuWiki.
Screenshot:
On the very top left you see the title of the page. On the right you see the title of this wiki installation. In the second line you see a grey-blueish bar with some buttons. Let's go through them one by one.
The third line starts with the word 'Trace:”. After that is a list of pages that you've just read, like the history function in your browser. Read breadcrumbs for more info.
Note that another kind of breadcrumb is available, which displays the hierarchy of namespaces the current page is in. See the youarehere configuration setting.