An example User Control used for "Load control after installation" when creating an Umbraco package. (See http://issues.umbraco.org/issue/U4-7471)

uWhiteLabel.Install.InstallControl.ascx

<%@ Control Language="C#" AutoEventWireup="true" Inherits="uWhiteLabel.Install.InstallControl" %>
<div>
    <h3>uWhiteLabel Installed Successfully!</h3>
</div>
<hr />
<div>
    <p class="umb-abstract">Instructions</p>
    <ol>
        <li>...more stuff here...</li>
    </ol>
</div>

uWhiteLabel.Install.InstallControl.cs

using System;

namespace uWhiteLabel.Install
{
    public class InstallControl : System.Web.UI.UserControl
    {
        protected string Test;
        protected void Page_Load(object sender, EventArgs e)
        {
            //you could do stuff here if you wanted
        }
    }
}