Set up your computer to display the screen that you want to capture. For example, if you want to take a picture of your Web site, open your home page in the browser.
Press the Print Screen button on your keyboard. This captures a "Snapshot" on the Clipboard.
Open a graphics program, such as MS Paint. Press "Control + V" on your keyboard.
You can add details to your image, edit image size, get rid of the part that don't need
Save the image.
When you save it, selet the save type to png.
FREE Graphic Programs
Paint.NET - You need .NETFramework to run it