When creating an order, you can set the Order Type. Order types are created in the r_keeper manager module.

If the "Default Order Type" is configured for an Order Category, the Order Type corresponding to the selected Order Category will be automatically set (the "Default Order Type" property of the Order Category is supported).

To change the Order Type, select the desired one from the list. 

Only Order Types allowed for the selected Order Category will be available for selection (the Order Category property "Use Order Types" is supported)

Depending on the value of the Order Type is required parameter, selecting an Order Type may be mandatory or optional.
If the Order Type is required, then without selecting it, an order cannot be created.