Mac OS X Finder FAQ: How do I open a new Mac Finder window using the keyboard?
Mac Finder keyboard tips - keystroke to open a new Finder window
To open a new Mac Finder window using the keyboard, make sure a Finder window is currently the foreground application, then press the [Command][n] keystoke. This will open a new Mac Finder window, and is equivalent to clicking the File menu, and then clicking the New Finder Window menu item. (It's also much faster.)