User controls are created using .ASCX in ASP.NET.After .ASCX file is created you need to two things in order that the ASCX can be used in project:.
Register the ASCX control in page using the <%@ Register directive.
<%@ Register tagprefix="Accounting" Tagname="footer" Src="Footer.ascx" %>
Now to use the above accounting footer in page you can use the below directive.
<Accounting:footer runat="server" />