Step 1: Create aspx page as like below
Default.aspx

Step 2: Copy the following code in cs file of Default.aspx

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;
using System.Data;
using System.Configuration;

namespace LinQExAmple
{
    public partial class _Default : System.Web.UI.Page
    {
        public DataSet ds;
        string connectionstring = ConfigurationManager.ConnectionStrings["TestConnectionString"].ConnectionString;
        protected void Page_Load(object sender, EventArgs e)
        {
            TxtId.Enabled = false;
        }

        protected void btnSelect_Click(object sender, EventArgs e)
        {
            TestDataContext db = new TestDataContext();
            var user = from u in db.Users
                       where u.Userid==Convert.ToInt32(TxtName0.Text)
                       select new
                       {
                           brand=u,
                       };
            foreach (var a in user)
            {
                TxtId.Text = a.brand.Userid.ToString();
                TxtName.Text = a.brand.Name.ToString();
            }
            TxtId.Enabled = false;
        }

        protected void btnInsert_Click(object sender, EventArgs e)
        {
            TxtId.Enabled=false;
            TestDataContext db = new TestDataContext();
            User u1 = new User { Name = TxtName.Text };
            db.Users.InsertOnSubmit(u1);
            db.SubmitChanges();
            Response.Redirect("Default.aspx");
        }

        protected void btnEdit_Click(object sender, EventArgs e)
        {
            TestDataContext db = new TestDataContext();
            User user = db.Users.First(u=>u.Userid==Convert.ToInt32(TxtName0.Text));
            user.Name = TxtName.Text;
            db.SubmitChanges();
            Response.Redirect("Default.aspx");
        }

        protected void btnDelete_Click(object sender, EventArgs e)
        {
            TestDataContext db = new TestDataContext();
            User user = db.Users.Single(u => u.Userid == Convert.ToInt32(TxtName0.Text));
            db.Users.DeleteOnSubmit(user);
            db.SubmitChanges();
            Response.Redirect("Default.aspx");
        }

        protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
        {
            if (e.CommandName.Equals("Edits"))
            {
                int index = Convert.ToInt32(e.CommandArgument.ToString());
                id = Convert.ToInt32(GridView1.DataKeys[index].Value);
                TxtName0.Text = id.ToString();
                TxtName.Text = id.ToString();

                SqlConnection mycon = new SqlConnection(connectionstring);
                SqlCommand mycmd = new SqlCommand("SELECT [User].* FROM[User] where userid='" + TxtName0.Text + "'", mycon);
                SqlDataAdapter myadpt = new SqlDataAdapter(mycmd);
                DataSet ds = new DataSet();
                myadpt.Fill(ds);
                TxtId.Text = ds.Tables[0].Rows[0]["UserId"].ToString();
                TxtName.Text = ds.Tables[0].Rows[0]["Name"].ToString();
            }
        }

        protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
        {
            e.Row.Cells[0].Visible = false;
        }
    }
}

Also see my other blog: TreeView using database
                                                            Get Primary key of gridview on edit commant
                                       Reset Table id to zero in sql server and many more.