Working with ascx and sitefinity is very straightforward once you know the exact things to do to make it work.
1. I have a header control header.ascx, footer control footer.ascx and a main content like AdminScorecard.ascx page.
2. can you please tell me how i need to arrange all three controls on a single page.
What I suggest is that you create a master page for your pages and place all these controls unto your template page or if you prefer adding them to every single page then go ahead.
But to start you should have a template having a content place holder such as
<asp:ContentPlaceHolder ID="ContentPlaceHolder1" runat="server" />
then when you select this template you will be able to add your ascx controls to this place holder.
To add your controls to the page, you can do it in 2 ways:
1- Uploading your control in sitefinity Add Controls Panel then Upload Control
2- modify the web.config
<add name="ControlName" section="My Controls" type="Full Qualified Name, Assembly Name"/>
3. In my AdminScorecard.ascx page i have a button when i click on that button it should redirect to another page. Could you please tell me how i need to do this (in .net we write Response.Redirect(Home.aspx). In sitefinity how i need to do this.
You need to create this type of controls in visual studio and add code behind to it with the Response.Redirect on button click then upload your control as i stated before.
4. how i need to pass the values through query string, cookies.
Same as point 3.
Hope this helps,