The code thats working is below.
<!DOCTYPE html>
<html>
<head>
<script src="jquery.js"></script>
</head>
<body>
<p>HI How are you. ? </p>
<p>HI How are you. ? </p>
<p>HI How are you. ? </p>
<p>HI How are you. ? </p>
<button id="myButtonId">Click Me</button>
<script>
$(document).ready(function(){
$("button").click(function(){
$("p").hide();
});
});
</script>
</body>
</html>
If you observe, I have just moved the script tags around.