Operating a computer would be difficult if you didn't constantly receive visual feedback showing you what your machine is doing. This vital function is provided by your computer's monitor.
The traditional computer monitor is a lot like a little television set. Your microprocessor electronically transmits words and pictures (text and graphics, in PC lingo) to your monitor, in some approximation of how these visuals would appear on paper. You view the monitor and respond according to what you see onscreen.