asp.net MVC4 -- error messages ?

How can I change the below
\Views\Shared\Error.cshtml (etc)
to display REAL error messages ?
------------------------------------------------------------------------
@model System.Web.Mvc.HandleErrorInfo

@{
    ViewBag.Title = "Error";
}

<hgroup class="title">
    <h1 class="error">Error.</h1>
    <h2 class="error">An error occurred while processing your request.</h2>
</hgroup>
------------------------------------------------------------------------
I added the below to
\Views\Shared\Error.cshtml
but it did not work.

  Exception exc = Server.GetLastError();

    if (exc is HttpUnhandledException)
    {
        if (exc.InnerException != null)
        {
            exc = new Exception(exc.InnerException.Message);
            Server.Transfer("ErrorPage.aspx?handler=Application_Error%20-%20Global.asax",
                true);
        }
    }