If you want to be able to connect to your webservices from the Workflow Designer you must have a SOAP webservice.
First add the webservice in the "Webservices" page, in your configurations, and test the connection to your webservice.
Personnally I usually do webservices in .asmx (ASMX) or .svc (WCF) using SOAP. The methods are automatically found by DocuWare in your workflows.
Hope it helps