You need only put the war file to webapp server and add to the page as an portlet.
If you're a newbie, you can follow the gatein document to find a way how to add an application to page at here http://docs.jboss.com/gatein/portal/3.1.0-FINAL/user-guide/en-US/html/
I only mention that you must use Orbeon Professional Edition, because Community version haven't supported that use Orbeon as a portlet
Thank you, Khoi! Will do so. Thank you for the link of the documentation as well.