The keyboard is the main way to interact with a computer. One presses a button with a finger and a letter, number or character is entered into the program. This is the way one types a new document, sends an e-mail, enters a website address and even directs a character in a video game.
The Mouse is the tool you use to navigate throughout a computer. You use the Mouse to click an icon to open a program, document or item, adjust volume, play games and more. The Mouse is used the following way: you click the left mouse key to select and open a file, and use the right mouse key to open up the menu for that item. The menu allows you to change certain properties of the item, or to move the item to another part of the computer.
The Monitor is the display you use to view everything that happens when you interact with the computer. The Monitor comes in various sizes, from under 9 inches all the way to 30 inches. Even more monitors are bigger. The type of monitor you wish to get for your own computer depends how comfortable you are with your vision.