An assignment rule is a logical collection of business conditions, and Assignment Manager evaluates potential candidates based on these rules. Below is the description of the Assignment Rule Creation.
Navigation: Site Map > Assignment Administration > Assignment Rule list
Create Rules
• Select the Assignment Object(s) to be assigned by this rule

Introduction to the Assignment Policies
Siebel applications include predefined assignment policies for each of the predefined assignment objects. You should use these predefined assignment policies, however, you can also create new assignment policies for dynamic assignment. If you plan to use the predefined assignment policies, you must first activate them.

Introduction of Assignment Manager :  Siebel Assignment Manager routes business entities and work items to the most appropriate candidates by enforcing business rules set by sales, service, and marketing organizations. Assignment Manager does this by matching candidates (that is, employees, positions, and organizations) to predefined and user-configurable assignment objects. To assign the most qualified candidate to each object, Assignment Manager applies assignment rules that you define to each candidate.