<asp:HiddenField ID="HiddenField1" runat="Server" Value="This is the Value of Hidden field" />
            <asp:Button ID="Button1" runat="Server" OnClick="ChangeLabelText" Text="Change Label Text to Hiidden Field Value" />                                        
                    
            // CODE BEHIND
            // Fires when Button is clicked
            protected void ChangeLabelText(object sender, EventArgs e)
            {
                Label1.Text = hiddeFieldValue.Value;
            }