Using HttpClient or RestClient is preferred. SOAP involves sending specially formatted XML. Once you figure out the contents of the XML, it should be simple to start using HttpClient or RestClient.
If you really want to continue using SOAP, you can do the following:
Add an empty library to your target called soapclient.
Right click on the new library and choose 'Import PB Extension...'
Choose the file pbsoapclient126.pbx.
Now you have all the interface objects in a PBL instead of a PBD. You will have to deploy pbsoapclient126.pbx with your app.