I assume that you are in the Finder. Command+Opt+Up Arrow opens the folder directly the one you are currently in in a new window. Command+Opt+Down Arrow opens the current selection in a new window.
If you do the same without the option key, the folders open in the same window
Edit: As most of your recent posts are about iTunes, the following applies there:
Cmd+Opt+Up or Down = Toggles mute on and off
Cmd+Up = Volume up
Cmd+Down = Volume down