You can create an identifier from the property sheet of an entity.
Open the Attributes tab in the property sheet of an entity, select one or more attributes, and click the Create Identifier tool. The selected attributes are associated with the identifier and are listed on the attributes tab of its property sheet.
Open the Identifiers tab in the property sheet of an entity, and click the Add a Row tool.
For general information about creating objects, see Core Features Guide > The PowerDesigner Interface > Objects.