how to use web User Control in asp.net

Add A web user control file and write code for that control

Add Place Holder in .aspx file
<asp:PlaceHolder ID="ControlPlace" runat="server"></asp:PlaceHolder>

Add line <%@ Reference Control="~/UserControls/ScoreCardControl.ascx" %>  in .aspx file in which you want to use the web user control.

In .aspx.cs file-
make object of user control in .cs file
  private UserControls_ScoreCardControl controlObj = new UserControls_ScoreCardControl();
load control
controlObj = (UserControls_ScoreCardControl)LoadControl("~/UserControls/ScoreCardControl.ascx");
 ControlPlace.Controls.Add(controlObj);