If you're a new Mac user, an ex Windows user or just want to use the facility of right clicking on your Mac (to bring up pop-up menus with relevant options) then here's how to do it:

To enable right click without changing settings:

You can 'right click' on any item by pressing the Ctrl key and clicking the mouse. This will execute a right mouse click on the item, and will usually bring you up a pop-up menu with options of what to do. Try it on a file or folder in Finder to see what I mean.

To enable PROPER right clicking with a Mac mouse:

Although it only appears to have 1 large button, the Mac mouse actually has a left and right mouse button - just all formed from one piece of plastic. To enable right clicking with this button, see the steps here:
http://theappleblog.com/2008/08/21/mac-101-enable-right-click-on-macs/