If you have the C# file in the project, you are done.  Just reference the
class name in your code.  I created a web service called MathClass which had
a method called AddInts.  In the windows form code, I just referenced the
class (MathClass.cs file created by wsdl).

...
       MathClass myMathClass;
       int myResult, v1, v2;

       public Form1()
       {
           InitializeComponent();
       }

       private void button1_Click(object sender, EventArgs e)
       {
           myMathClass = new MathClass();
           v1 = Int32.Parse( textBox2.Text );
           v2 = Int32.Parse( textBox3.Text );
           myResult = myMathClass.AddInts( v1, v2 );

           textBox1.Text = myResult.ToString();
       }