How to use update panel in asp.net

<asp:ScriptManager ID="ScriptManager"
                   runat="server" />
<asp:UpdatePanel ID="UpdatePanel1"
                 UpdateMode="Conditional"
                 runat="server">
    <ContentTemplate>
       <fieldset>
       <legend>UpdatePanel content</legend>
        <!-- Other content in the panel. -->
        <%=DateTime.Now.ToString() %>
        <br />
        <asp:Button ID="Button1"
                    Text="Refresh Panel"
                    runat="server" />
        </fieldset>
    </ContentTemplate>
</asp:UpdatePanel>