Is there any examples other than the one in youtube ,which explains about External data source and external objects.Is it possible to get the details of another salesforce org like details of account using this feature?
As usual, the "forward looking statement" safe harbor caveats apply to this response. :-)
External objects are currently (June 2014) in a limited pilot with plans currently to go to beta in Summer 14. If you are interested in using this feature, you should reach your AE or Customer Success contacts and see about enrolling in the pilot.
I just checked my pre-release org, and currently there doesn't appear to be anything that would enable or use this feature. If the plans for beta do follow through into reality, I would expect some parameters in your org setup to enable this, along with a user/developer guide to assist you with implementing it.