Relationship between WebHostBuilder, Kestrel and IIS

Hi,

in ASP.NET Core a Web App is with RC2 a simple Console Application.  In Programm.cs there is by default the following Code in it: 

public class Program
{
  public static void Main(string[] args)
  {
      var host = new WebHostBuilder()
          .UseKestrel()
          .UseContentRoot(Directory.GetCurrentDirectory())
          .UseIISIntegration()
          .UseStartup<Startup>()
          .Build();

      host.Run();
  }
}

How is the Relationship between WebHostBuilder, Kestrel and IIS. Are they any Resources that explain the interaction between them?
Which Component creates the HTTPContext-Object?

Regards,
Chantal