Untitled

<!DOCTYPE html>
<html>
<head>
	<title>class</title>

	<style>
	.rect{
		position: absolute;
		width:50px;
		height:50px;
		background:red;
	}
	html, body {
		height: 500;
	}
	</style>

	<script type="text/javascript">
	function createRect(e) {
		e = e || window.event; //для IE - window
		var div = document.createElement('div');
		div.className = "rect";
		div.style.left = e.clientX + "px"; //координата относительно текущего окна
		div.style.top = e.clientY + "px";
		document.body.appendChild(div);
	}
	</script>
</head>
<body onclick="createRect(event)">

</body>
</html>