In Windows hold down ALT and press the Print Screen key. Let them both up. Then in a graphics program, like MS Paint, hold down your Control key and press V. It should paste to your MS Paint.
Your Print Screen key is on the upper right of your keyboard and may say PRTSCN or something similar.
There are much better graphics programs than MS Paint. You can get a 30-day trial of Paint Shop Pro on the Corel website.
With a little work, you'll have an avatar like mine