Just make a new instance of the "Service1SoapClient", like this:
Service1SoapClient myWS = new Service1SoapClient();
Then, you should see your methods on the "myWS" variable:
string sResult = myWS.CelsiusToFahrenheit("25");
You may have to include the namespace, if you did not put it in the "using" section:
ServiceReference1.Service1SoapClient myWS = new ServiceReference1.Service1SoapClient();
However, after you have instantiated the class, you can call the methods on it.