Currently Being ModeratedFeb 12, 2013 1:16 AM (in response to EDLIU)
Both are easy to do. Mac laptops have had this ability for about 22 years, and Mac desktops for 25 years.
The MacBook Pro and the iMac (if recent) use Mini DisplayPort for external monitors. All you need is a cable that has Mini DisplayPort on one end, for the Mac side, and on the other end it needs whatever connector the monitor has (could be DVI, VGA, HDMI, or DisplayPort). You can get the cables at Apple, Amazon, or Monoprice.com with the latter being cheaper.
You can plug in the monitor while the computer is running. To customize the monitor resolution, color profile, and other options, you go into the Displays system preference. You also use Displays to customize the arrangement. For example, if you placed the monitor to the right of the Mac, you can move monitor icons to tell the Mac that the external is on the right. That way, when you move the mouse off the right edge of the Mac, it appears at the left edge of the external monitor.