A left-click is actually called clicking the left mouse button of the mouse. If seen, ” left-clicking ” only means that when you click the left mouse button, which is actually by default also the primary button.
This term “left-click” is often used in contrast to “right-click” which means to click the secondary button of the mouse which is in the right side of the mouse.
Left-clicking is used to perform many common computer tasks, such as to select objects, to open hyperlinks, and to close Windows. Similarly,
if you click the left mouse button and hold to drag then it can be used to select text or to do drag and drop operations.
In video games, left-clicking is typically used to perform a primary action, such as to move a character or fire a weapon.
For right-handed users, this left-click is quite a natural click, as it is done by their index finger. For left-handed users, it may be a little awkward to do it. So both Mac OS X and Windows allow you to switch primary mouse button from left to right.