Hi Manoj,
WSDL is web service description language. every web service is has WSDL.
As you need to expose your interface as webservice and sender will consume the service. you can retrieve the wsdl from sender agreement/ICO (display wsdl option). Then provide the wsdl and webservice url to sender.
refer the below wiki
Generating Web Service From PI - Contributor Corner - SCN Wiki
regards,
Harish