You must have a webservice like this http://localhost/MyWebService.asmx
For retreive your webservice wsdl you must put this address at the browser address bar: http://localhost/MyWebService.asmx?wsdl
If you want to use this wsdl, you must go to the visual studio and add web reference with the wsdl address. You can also, generate your service proxy by command-line, executing: wsdl.exe http://localhost/MyWebService.asmx?wsdl
Check your configuration file for this setting:
The httpGetEnabled attribute must be set to true.
I suppose you are using WCF