On Insert, update or delete whole page is reloading in asp.net c#

As Shridhar Gowda says you need to use updatePanel control if you wish to refresh a part of page instead of reloading whole page.Here I am giving you a sample code.

In .aspx

<![CDATA[<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"
    CodeBehind="Default.aspx.cs" Inherits="WebApplicationUpdatePanel._Default" %>]]>

<asp:content id="HeaderContent" runat="server" contentplaceholderid="HeadContent" xmlns:asp="#unknown">
</asp:content>
<asp:content id="BodyContent" runat="server" contentplaceholderid="MainContent" xmlns:asp="#unknown">

    <asp:scriptmanager id="ScriptManager1" runat="server">
    </asp:scriptmanager>
    <asp:updatepanel id="UpdatePanel1" runat="server">
    <contenttemplate>
    <asp:repeater id="Repeater1" runat="server">
    <HeaderTemplate>

    <table style="border:1px solid #0000FF; width:500px" cellpadding="0">

    <tr style="background-color:#FF6600; color:#000000; font-size: large; font-weight: bold;">

    <td>

    ID

    </td>

        <td>

    NAME

    </td>

        <td>

    Roll

    </td>

    </tr>

    </HeaderTemplate>
     <itemtemplate>

    <tr style="background-color:#EBEFF0">

    <td>
   <asp:label id="lblID" runat="server" text="<%#Eval("ID") %>" />
    </td>
        <td>
<asp:label id="lblName" runat="server" text="<%#Eval("Name") %>" />
    </td>
        <td>
    <asp:label id="lblRoll" runat="server" text="<%#Eval("Roll") %>" />
    </td>
    <tr>
     </tr></tr></itemtemplate>

    <footertemplate>

    </footertemplate></table>

    
    </asp:repeater>
    
  

    </contenttemplate>
    <triggers>
    <asp:asyncpostbacktrigger controlid="btnAdd" eventname="Click" />
    </triggers>
    </asp:updatepanel>
      <h3>Entry</h3><br />
      <asp:label id="lblmsg" runat="server" forecolor="Green"></asp:label>
    Name<asp:textbox id="txtName" runat="server"></asp:textbox><br />
      Roll<asp:textbox id="txtRoll" runat="server"></asp:textbox><br />
            <asp:button id="btnAdd" runat="server" text="Add" onclick="btnAdd_Click" />
</asp:content>

In Code behind(.cs)

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

namespace WebApplicationUpdatePanel
{
    public partial class _Default : System.Web.UI.Page
    {
        BooksDBEntities db = new BooksDBEntities();
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                BindToRepeater();
            }
        }

        void BindToRepeater()
        {
            Repeater1.DataSource = db.Students.ToList();
            Repeater1.DataBind();
        }

        protected void btnAdd_Click(object sender, EventArgs e)
        {
            if (txtName.Text != "" && txtRoll.Text != "")
            {
                string name = txtName.Text;
                string roll = txtRoll.Text;

                Student s = new Student();
                s.Name = name;
                s.Roll = roll;

                db.Students.AddObject(s);
                db.SaveChanges();
                lblmsg.Text = "Successfully Updated!";
                BindToRepeater();
            }
        
        }
    }
}

Hope it helps.And have look in Microsoft's msdn following link
<a href="https://msdn.microsoft.com/en-us/library/bb399001%28v=vs.140%29.aspx">Introduction to the UpdatePanel Control</a>