As you know that in 3 tier architecture there are three layers

1. User interface layer. (Is our Form in Windows application and .aspx page in Web application)
2. Data Access layer. (Which provides interface between Business logic layer and Database)
3. Business Logic layer.(Which stores your application logic)

Step 5: Now add reference in to BusinessLogiclayer  

Step 6: And last Add reference to UserInterfacelayer

Here we add two references Businesslogiclayer and DataAccesslayer. So your window will look like this,

Page will look like this in browser



Step 8: In DataAccesslogiclayer add LINQ TO SQL class name test.dbml

namespace BusinessLoggiclayer
{
    public class REGISTER
    {
        #region "Private variable"
        string _FNAME;      
        string _LNAME;     
        string _EMAILID;      
        string _PASSWORD;       
        #endregion 

        #region "Public Property"
        public string FNAME
        {
            get { return _FNAME; }
            set { _FNAME = value; }
        }
        public string LNAME
        {
            get { return _LNAME; }
            set { _LNAME = value; }
        }
        public string EMAILID
        {
            get { return _EMAILID; }
            set { _EMAILID = value; }
        }
        public string PASSWORD
        {
            get { return _PASSWORD; }
            set { _PASSWORD = value; }
        }
        #endregion

        #region "Public Method"
        public void Insert()
        {
            using (testDataContext db = new testDataContext())
            {
                db.sp_REGISTER(1, _FNAME, _LNAME, _EMAILID, _PASSWORD);
            }
        }
        #endregion
    }
}

Step 11: Write code in Register.aspx.cs

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq; 

#region "Private Using"
using BusinessLoggiclayer;
#endregion 

public partial class Register : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        if(!IsPostBack)
        {
        }
    }
    protected void Btnregister_Click(object sender, EventArgs e)
    {
        REGISTER r = new REGISTER();
        r.FNAME = txtfname.Text;
        r.LNAME = txtlname.Text;
        r.EMAILID = txtemailid.Text;
        r.PASSWORD = txtpassword.Text;
        r.Insert();
    }
}