Screenshots come in handy when reporting errors, creating tutorials, and creating image snippets to serve as reminders. How to take a screenshot will depend on what type of computer or device you are using. Below are some common ways to take screenshots.
PrtScn/SysRq Capture the screen to the clipboard
Alt-PrtScn/SysRq Captures only the currently active window and copies it to the clipboard.
In Windows 7, you can use the “Snipping Tool” found in “Programs” to take screenshots and screen snippets.
Shift-Command-3 Capture the screen to a file
Shift-Control-Command-3 Capture the screen to the Clipboard
Shift-Command-4 Capture a selection to a file
Shift-Control-Command-4 Capture a selection to the Clipboard
iPhone, iPod Touch, iPad
Hold the “Home” button and press the “Sleep/wake” button on the top of the phone. The screen will flash white and if your volume is turned on, you will hear the same sound you hear when you take a picture.
Your screenshot will appear in the Camera Roll of your “Photos” app.
External Resource: http://take-a-screenshot.org/