usercontrol .ascx file

The easiest way is to add a user control to a webpage by simply dragging it from Solution Explorer to a webpage in Design view. When you add the user control to a page, you can see the control’s visual makeup in Design view. If you switch to Source view, you can see the markup information that Visual Studio added to your page

It can also be done manually by doing two things:
Add the following line in the aspx page just after the Page directive:

<%@ Register src="UserControl.ascx" tagname="UserControl"
tagprefix="uc1" %>

Then you can start using the control within the form tag like any other aspnet control as shown below:

<uc1:userControl ID="userControl1" runat="server"
someTypeProperty="Home" />

Please go through this msdn link for more information http://msdn.microsoft.com/en-us/library/sbz9etab.aspx[^]
Hope this helps.