Sometimes you may want to print out, or send a copy, of what is on the screen, for example a list of files in Windows Explorer, but Windows Explorer doesn’t have a print function, so how do you print it? You can use the Print Screen function to take a screenshot and then print the screenshot.
The way to take a screenshot is to press the Print Screen key on your keyboard (which may be abbreviated to something like ‘PrtScn’). That takes a shot of the whole screen, but holding down the [Alt] key when you press Print Screen takes a screenshot of just the window which is in focus.
The screenshot is initially hidden away on the Windows clipboard, so from there you have to start a program capable of taking pictures (such as Start > All Programs > Accessories > Paint) and paste the picture into it by pressing [Ctrl]+[V], then print or save the result.