The trash can is in the bottom right corner of your screen. You can even think of your desktop pattern or picture as the blotter on your desk. The drawers holding your pens, pencils, files, etc. are the folders and utility files on your hard drive. In that same vein your desk lamp is your monitor. You computer can run without a monitor you just would know what it is doing and how to tell it what to do.
Monitors have certain capabilities which include resolution and colors.
Depending you what model of computer you have your machine may be able to show you anywhere from 256 colors to millions of colors on screen. The more colors offered the clearer and cleaner your screen images look. Some of the more costly computers are able to make images clearer by increasing the amount of image you see on the screen. To do this it will make images on the screen smaller. This is determined by the resolution of your monitor.