With domain is meant a product group or cost centers.
Open the Domains designer from the navigation pane.
Create a new domain model by clicking New Model from the ribbon menu Main. In the property pane, give the model a name.
With drag & drop, you can place a domain element from the element repository onto the canvas. It is possible to rename the domain by double-clicking the domain element. For the domains, you can also add groups, e.g., for different products, etc.
Click Save from the ribbon menu Main.
In the save-dialog select a scope (or create a new one) and click Save.