Where is the binding with the wsdl/soap file and the code behind of the web service?

I want to understand the connection between the wdsl file and the code that really do the methods decripted by the wsdl file. So I ask you, where is the url reference to the code in the wsdl file? How can the web service get the methods when I add a reference of this to my code (for example c#)? Thank you in advance.