How Can I Add Cookies On My Given Code.Please Help Me By Editing My Code.

using System;
using System..Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
namespace logindemo
{
    public partial class login : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void TextBox1_TextChanged(object sender, EventArgs e)
        {

        }

        protected void Button1_Click(object sender, EventArgs e)
        {
            string connetionString = "Data Source=INFND-DTP-0493;Initial Catalog=Test_DB;User ID=alok;Password=abcd@1234";
            SqlConnection conn = new 
            SqlConnection(connetionString);
            conn.Open();
            string commText = "Select * from login where User_name='" + TextBox1.Text.Trim() + "' and Password='" + TextBox2.Text.Trim() + "'";
            SqlCommand cmd =new
            SqlCommand(commText, conn);
            SqlDataReader dr = cmd.ExecuteReader();
       
            if (!dr.Read())
            {
                Response.Write("Invalid User");
            }
            else
            {
                conn.Close();
                Session["Username"] = TextBox1.Text;
                Response.Redirect("WebForm1.aspx");  

            }
            /*else
            {
                conn.Close();
                Response.Redirect("~/welcometo.aspx");
            }*/

        }

        protected void Button2_Click(object sender, EventArgs e)
        {
            TextBox1.Text = String.Empty;
            TextBox2.Text = String.Empty;
        }

        protected void Button3_Click(object sender, EventArgs e)
        {
            Response.Redirect("~/Register.aspx");
        }
    }
}