Although clicking is the most common way to use the mouse, the second most common way is called double-clicking. Double-clicking means pressing and releasing the left mouse button (or trackpad button) twice in rapid succession. Double-clicking is basically a shortcut for eliminating multiple single clicks to select an item and then choosing a menu command. For example, to open a file, you typically need to follow four steps:
Move the mouse pointer over the file you want to open.
Click the file to tell your Macintosh that this is the file you want to open.
Click the File menu title. A pull-down menu appears.
Click the Open command. (From now on, this book will explain how to choose a menu title and a command by using the shorter description: "Select File▸Open.")
Rather than click the mouse three different times, you could open a file just by double-clicking the mouse:
Move the mouse pointer over the file you want to open.
Double-click the file to tell your Macintosh that you want to open it.