One thing that new users to the Mac OS might not know about is the option key and how it is used with the menu bar. If you go to the sound preference in system preferences you are given the option to Show Volume in the Menu Bar. When you click on the Sound Icon you can increase or decrease the volume.
Click on the same Sound Icon with the option key down and you have the ability to change input and output devices. This also works with other menu items, such as Wifi.
