This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
Rather than giving you the answer straight up, I'll assume you want to do this from the command line. So type jar at the command line and you will get a screen of usage information for this command plus a couple of examples as well. Try it and see how you go.