Javascript - random color generator [on hold]

I found this piece of the code online and I know its a function to generate random colors in JavaScript and I want to use it but I don't understand it completely. It'd be great if someone gave me an elaborated explanation.

function getRandomColor() {
  var letters = '0123456789ABCDEF'.split('');    
  var color = '#';    
  for (var i = 0; i < 6; i++ ) {        
      color += letters[Math.floor(Math.random() * 16)];    
  }
  return color;
}