If you are seeing some thing interesting on the iPad screen then you would want to capture that moment before it's gone. Screenshot is quiet use if you have an error on your device and you want to capture an image so that later you could show it to a support person and they could assist you in fixing the issue. Here's how:
1. While you are looking at the screen press Sleep/Wake + Home button and quickly let go of the buttons.
You will see the screen quickly flashes indicating that it has taken the photo.
Your capture should now be placed in the Camera Roll album. To view the photo go into the album and open it up. Once you have the image you could email it your friend if you like.