Unlike the others, I'm not going to go into details about the WSDL file and how you can read it. You will eventually learn all of that by yourself by reading books, articles, experimenting with web services etc.
What I'm going to do is recommend you a very simple to use, yet powerful tool, than must be in the toolbox of every web service developer (especially someone new to web services): SoapUI.
You create a simple project in SoapUI and point it to the WSDL file of the web service. It will discover the operations, create sample request and response messages, create mocks of the web service and much more.
You can then look at the WSDL code and with the help of what's presented inside SoapUI discover which elements are involved in each method.