(newbie) editing html elements from php form data ?? any one ?

hi, i'm a newbie to php, i'm writing a a script right now but i'm stuck at this situation..

i want visitors to edit a specific html elements through a form in another page coded with php or any other suitable language for this purpose

explanation:

let's say the index.html page has a paragraph like

<p>this is a paragraph</p>

i want visitors to edit this paragraph through a form like:

Paragraph : |___________|

[submit]

i hope you get the question and answer it quickly cuz I'm in grave need of it..
thank you in advance