OS X Mountain Lion
When you open a folder in a Finder window, the folder’s contents usually replace the current contents of the window. If you need to copy or move items between folders, or perform other tasks, you can open multiple Finder windows.

Note: If you’ve hidden a Finder window’s toolbar and sidebar, then double-clicking a folder in the window opens the folder in a new window.

Open a specific folder in a new window

  • To open a specific folder, press the Command (⌘) key while you double-click the folder’s icon.
  • To open a new Finder window without opening a specific folder, choose File > New Finder Window or press Command (⌘)–N.

Open all folders in new windows

  1. Make sure you’re in the Finder by clicking the desktop (the background area of your screen).
  2. Choose Finder > Preferences, and then click General.
  3. Select “Always open folders in a new window.”