A click is defined as pressing the mouse button down and without delaying release it again.
On a Mac, drag CDs and DVDs to the Trash to eject them.
Set the number of colours your monitor should use.
On Mac OS 9, how to find out your screen’s resolution.
USB is the Universal Serial Bus, used for plugging in many devices, such as printers and keyboards.
Ports are the various places where you can plug things in to your Mac: a keyboard, scanner, printer, speakers, a joystick — whatever.