Seems like you are well away.
So you have two php files.
One is the class file because you should have it seperate.
The other is the index.php file say.
in your index.php have.
//if new window then start sessions to store objects
$_SESSION['set'] = new SetClass();
//Value of text to be inserted comes from a post say
My post is very basic and shows nothing of the HTML wrapped around the index.php page nor does it show any sanitization etc.