An example of fillRect, clearRect and strokeRect

function drawShape(){
  // get the canvas element using the DOM
  var canvas = document.getElementById('tutorial');

  // Make sure we don't execute when canvas isn't supported
  if (canvas.getContext){

    // use getContext to use the canvas for drawing
    var ctx = canvas.getContext('2d');

    // Draw shapes
    ctx.fillRect(25,25,100,100);
          ctx.clearRect(45,45,60,60);
          ctx.strokeRect(50,50,50,50);
		  ctx.fillStyle=("rgba(25, 100, 250, 0.3)");
		  ctx.beginPath();
		  ctx.moveTo(75,75);
		  ctx.rect(75,75,100,100);
		  ctx.fill();
  }
}