I use double quotes for HTML and single for PHP usually as it's easier for example:
<?php
$haidere= ":P";//This is a comment and you may see that I used a double quote for the variable thats just another thing I do, You can switch between the two.
echo '<html>
<head>
<title>
Ummm
</title>
</head>
<div id="You see here!">
<body>
HAHAHA DON\'T '; echo $haidere;
echo '
</body>
</html>';
?>
Also when something like the word "don't" needs a ' you will need to escape it by putting a \ in front of it so it doesn't interfere with the script.