Hi Bhushan, there is not a field called "Acceptance Criteria" in Agile Central -- unless, of course, one of your administrators added it as a custom field!
Typically though, users just add the Acceptance Criteria in the Description field of a User Story. Since the ability to create and share templates was added to the Editable Detail Page of a work item in Agile Central, it makes it a lot easier to set the format of the description field - both as a reminder to you and your users!
Take a look here and scroll down to the "Use Templates" section to see how to use templates: New Editable Detail Pages | CA Agile Central Help
I hope that helps!