animal.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

namespace work093
{
    public class Animal
    {
        private string _type;
        public void SetType(string type)
        {
            this._type = type;
        }


    }
}

webform1.aspx.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace work093
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            work093.Animal bird = new Animal();
            bird.SetType("BIRD");

        }
    }
}