How to take a screen shot under Ubuntu

Created by marcobra (Marco Braida)
Keywords:
howto take and save screenshot
Last updated by:
marcobra (Marco Braida)

I am a new user of Linux and just installed Ubuntu.
Which tool shall I use to take a screen shot and then save it as a file or paste it into a document?

https://answers.launchpad.net/ubuntu/+question/41111