Hi,
Case Assignment Rules—Determine how cases are assigned to users or put into queues as they are created manually, using Web-to-Case, Email-to-Case, On-Demand Email-to-Case, the Self-Service portal, the Customer Portal, Outlook, or Lotus Notes.
To create an assignment rule, from Setup, enter Assignment Rules in the Quick Find box, then select Lead Assignment Rules or Case Assignment Rules.
Now you can create your own assignment rule with its name and criteria.
Hope this helps you.