dynamic data manipulation in form

I have a script that I have written in PHP that is a basic form that inputs simple text into a mysql db. One section is just a textarea value that I would like to be able to add some dynamic formatting to the text being entered if the user wants. For example, I want to give the user the ability to be able to highlight the text and click on a paragraph tag and it automatically insert that tag - or a bold, itallic, underline, etc. I have searched the web but came up empty-handed. Any ideas? I don't even know where to begin. thanks, Doug