Create a new BP and add a receive activity, an empty activity, a reply activity, and any other activities required for the BP.
Expand the sub-process and drag the operation onto the empty receive activity.
Add links between the modeling elements in the main process and add business rules as needed.
Click Save.
If the sub-process is to be invoked as a synchronous request/reply web service, the Receive and Reply must be associated with the same partner, port type, and operation. These properties can all be configured in the property sheet for the user activity.