I won’t insult your intelligence by telling you what a keyboard does. Keyboards come in a range of prices to suit everyone. This ‘basic’ keyboard from a quality manufacturer HP/Compaq comes with several nice features and retails for just under $10.
This mouse too is really all you need, with two buttons and a scroll wheel in between to allow you to zip up and down scroll bars. This is again manufactured by HP/Compaq and retails for just under $5.
This mouse uses optical technology to eliminate the need for a mouse ball. The mouse ball is replaced with an optical sensor. That means no more dismantling and degunging of you mouse every couple of months. It retails for around twice the price of a standard mouse.
A tracker ball is like an upside-down mouse. The housing stays put, and the ball is moved by your fingers. The advantage is that you don’t run out of desk space as you do sometimes with a mouse when you want to move that bit further to the right, but you are up against the edge of your desk. They are a bit of a personal preference, so if you can borrow one from a friend before buying it to ensure that you actually like using it.