To help users manage their files, the Finder includes a specialized window, which is accessed by double-clicking the icon for the Mac OS X hard drive on the desktop.
Mac OS X introduces two modes of operation in the Finder window. The first of the two, single-window mode, is the toolbar version of the Finder. When the toolbar is present, double-clicking a folder opens the item you just clicked in the current window, replacing the previous contents.
The second mode, a toolbar-less version of the Finder window, can be entered by clicking the clear, oval-shaped toolbar button in the upper-right corner of the Finder window. In this mode, you can double-click folders to open additional windows . (We'll talk more about working with windows in the next chapter.)