Need help with building simple editor

I have just the basic skill of PHP and Javascript(Still not vary good at), and MySQL. I am trying to learn a bit about editing the “innerHTML” of a span tag. I saw a lot about it in the Ajax edit in place but that isn’t what I am looking for. I don’t know how to call the content to a text box for editing though and even then I still don’t know what to do after that so I REALLY need some direction here of I might just ruin something.