You should create a controller called CarsController, then add a public method Featured which returns a ViewResult passing in a list of featured cars.

public class CarsController : Controller
{
  private ICarService CarService;
  public CarsController(ICarService carService)
  {
    CarService = carService;
  }
  public ActionResult Featured()
  {
    var featuredCars = CarService.GetFeaturedCars;
    return View(featuredCars);
  }
}

Then you can create your view user control, call it Featured.ascx and put it in ~/Views/Cars/. It should be of type ViewUserControl<IEnumerable<Car>>.

Then in your main index view do the following <%= Html.RenderAction( "Featured", "Cars" ) %>

This will create your CarsController, call the Featured method, and render your Featured.ascx in place.

(You can ignore the bit about the CarService if you like, that's just to show a good testable design practice)