For obtaining access to CERN site, you need to register for this event under "Registration" (menu on the left).
The workshop will take place at IdeaSquare (building 3179).
You can find an interactive google-map here: http://goo.gl/WNSa6P.
You can collect your Visitors access cards at CERN's main reception (building 33) with the access code you have received by email if you haven't printed it already at home. Access to CERN site will be denied if you don't have it.