First try it WITH refresh.
You'll need to select a random text from your database (hint, use RAND() in your mysql request).
Once you know how to do that, learn how to make Javascript talk to your php page so you no longer need refresh. It's called AJAX, you can look at JQuery ( http://jquery.com/ ) for a library that will help you with it and specifically this page :
http://api.jquery.com/jQuery.ajax/
Your javascript will do a Ajax call to your php page, will get some data back and then will be able to display it in your page.
Look at the example, you should be able to do it from there.
But first do it with refresh, it's a first step.