Virtual desktops are an extremely useful feature of modern operating systems. It's a feature that provides some of the benefits of multiple monitors without the extra space or expense of adding more displays to your computer. Generally speaking the feature allows you to group together windows on one or more additional logical desktops without the need for multiple monitors.
On the Mac this feature is known as "Spaces" and was originally introduced way back in OS X 10.5 "Leopard", and was integrated into the Mission Control preference pane a couple of years later. This merge into Mission Control works very well, as long as you know where to look — because the preference pane doesn't really tell you where it is or how to find it.
To create a new space, or desktop you need to launch the Mission Control interface. This can be done either by pressing
F3 on a modern Mac (or
fn-F3 if you have your function keys enabled by default), pressing
ctrl-Up or by doing a 4-finger swipe up on a trackpad. Once you open up Mission Control you can see a plus sign on the far-right hand side of the screen. Clicking that will allow you to add a new Space to your Mac. You can add up to 15 new virtual desktops, to your system.
Once they're created you can switch between spaces a few different ways:
1. Four-finger Swipe: performing this swipe left or right will move you between desktops.
Ctrl-arrows: Holding down the ctrl key, and pressing the left or right arrow will move you between desktops.
Cmd-tab: Using the regular application switcher will move you to the first space where that application is open.
1. Mission Control: You can select a space directly from Mission Control to activate it.
Once you find it, this is a very useful feature, and can make operating on a smaller screen (like my 11" Macbook Air) a lot easier by allowing quick and easy context switches to move from browsers to text editors to terminal windows. It's something I definitely recommend if you've never tried it before.