There are many different programs available that will take a snapshot of your computer screen.  They have many different features and can be quite handy depending on your needs.  There is also a very simple one built right into Windows. Locate your Print Screen / System Request key, probably somewhere in the upper right corner of your keyboard.  Pressing this key will copy a picture of your screen to the clipboard.  You can then paste the image into a document or graphics program.  Pressing Alt+Print Screen will take a picture of the window that is currently in focus.  If you’ve never used this before, take a quick moment and give it a try.

Mac users can use Command+Shift+3 and Command+Shift+4 for simple screen captures.  Options for Linux users will vary depending on the installation, but the Print Screen key often works as described above.

Further Reading

Screen shot – Article from Computer Hope.com