You can use the built-in Snipping Tool in Windows to capture anything on your screen!
If you're not familiar with the Snipping Tool you will love it. Open the Start Menu and click on All Progams (at the bottom). Open the Accessories folder and right-click on Snipping Tool. Select 'Pin to task bar' and it will put a shortcut down on the task bar at the bottom of your computer screen for easy access.
Here's a 2-minute video that shows you how to use the Snipping tool.