How to call a dll file written in C# in asp.net

Simple C# source file is:

using System;

namespace Hello
{
    class HelloName
    {
      public void GiveGreeting(string name){
         Console.WriteLine("Hello "+name);
      }
      public string getGoodWish(string name){
         return "Good morning "+name;
      }
      
    }
}

This C# source file will be compiled into dll using command  csc /target:library HelloName.cs,
The method getGoodWish in class HelloName will be called in an aspx page like the following code.

aspx code is:
<%@ Page Language="C#" Debug="true" %>
<%@ Import Namespace="System" %>
<%@ Import Namespace="Hello" %>

   


   

       
       

       
       

       
       

        Function used in a variable:
       

        Function used as value for an object property:
       

        Function used as an argument in another function:
       

        Function used as an expression:
   

 My question is: I can't call the dll correctly, which step I made a mistake ?
                 where do I put the dll file ? So let IIS can find it?
                 Thanks for any valuable advice.