Exemplo de WebService
using System;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
[WebService(Namespace = "http://tempuri.org/")]
[WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
public class Service : System.Web.Services.WebService
{
    public Service () {
        //Uncomment the following line if using designed components
        //InitializeComponent();
    }
    [WebMethod]
    public double Soma(double n1, double n2) {
        return n1 + n2;
    }
}