I want to save an client-created string on an apache2 website

I recently set up an apache2-server for a schoolproject I’m working on. I would like the user to be able, to save a variable directly onto the website, therefore altering this part of the website forever or until the user changes it again. I know Python3, html, php and a bit of js. I realize, the information I gave you is not necessarily enough to really understand what I mean, but I am open to further questions. Help would be greatly appreciated, due to the project being due in a week from now, with extra extra-work still unfinished.
Thanks in advance,