From Mac Guides
Control-clicking on a Mac is equivalent to right-clicking on a Mac or in Windows. Control-clicking usually shows a menu at the location of the mouse cursor, known as a contextual menu.
To perform a control-click, hold down the control key on your keyboard (the one with "ctrl" or "control" written on it) and click the mouse. If you are using a two button mouse then right-clicking has the same effect.
Some actions can only be performed with a control-click, however Apple's Human Interface Guidelines state that every action that needs to be done should be able to be completed without needing to resort to using a contextual menu.