A touchpad is input device. A touchpad (also trackpad) is an area that imitates (does the same) functions of a computer mouse. There is no need of an external device like a mouse. The user just runs over the small sensitive pad with one or more fingers.
It is good to have the touchpad, because when the user is travelling, sometimes he or she cannot use a mouse. When the laptop is used at home, the user is able to attach (connect) a separate mouse.
New models of touchpads often have more functions because they are pressure-sensitive. Many have the function to scroll up and down a page or the volume field.
Most touchpads have the function of tapping, which imitates the left-click button on a mouse. The user can choose and change, which functions happen, if the user does certain moves. Example: The normal function for tapping on the pad is the left-click on the mouse. The user can change it in the settings section to the right-click of the mouse, if the user likes it better.