Asp Net UpdatePanel

I'm studying AspNet and I can not use the UpdatePanel in any way, I have a webform in a nested masterpage this is the code:

<%@ Page Title="Home Page" Language="C#" MasterPageFile="~/MasterPages/NestedMasterPage8Form.Master" AutoEventWireup="true" CodeBehind="Dashboard.aspx.cs" Inherits="WebApplication1._Default" %>

<asp:Content ID="BodyContent" ContentPlaceHolderID="MainContent" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server"></asp:ScriptManager>

<asp:UpdatePanel ID="UpdatePanel1" runat="server">

    <ContentTemplate>

       <asp:Label ID="Label3" runat="server" Text="Label"></asp:Label>

    </ContentTemplate>

    <Triggers>
        <asp:AsyncPostBackTrigger ControlID="Button1" EventName="Click" />
    </Triggers>

</asp:UpdatePanel>

<asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" />

This is the test code for the click event:

Label3.Text = "Aspx";

I have already tried in several ways with the button inside the ContentTemplate without indicating the Triggers but anyway the whole page updates when clicking the button, can you give me a light on the use of UpdatePanel?