When the computer is bought the main and generally most expensive item in this area has been acquired but there are many accessories that are needed for full and smooth functionality.
The computer generally has a touch pad but a mouse is a useful tool as it is often felt to be more easily able to move their pointer over and to the areas needed on screen.
It can be a USB Version mouse or a blue tooth or wireless mouse.
Standing computers need a key pad and there are different brands and people have particular preferences as to what they need from their keypad.
Again, a keypad can be plug in or wireless. If you are into gaming on the computer a dedicated graphics card may be a boon.