How to call a method in a different class.

This code generates the following error.   I'm new to c# and programming in general, so I'm not quite sure what needs to happen.

      public class confirm : System.Windows.Forms.Form    // this is the class that makes the call

private void button1_Click(object sender, System.EventArgs e)
            {
            AddOrder();     // this exists in       public class Form1 : System.Windows.Forms.Form


Here is the error I get, and both classes exist in POS.
            The name 'AddOrder' does not exist in the class or namespace 'POS.confirm

Thanks,
Sean