Adding tracelistener to web.config

I want to use below code with a website. Which config sections I should add to web.config to log the output into a file or windows eventlog ?

using System.Diagnostics;

// Singleton in real code
Class Logger
{
   // In constructor: Trace.AutoFlush = false;

   public void Log(message)
   {
       String formattedLog = formatLog(message);
       Trace.TraceInformation(formattedLog);
       Trace.Flush();
   }
}