Frontend to Backend Question

I’ve created front end forms for data entry. Data entered will be placed into a backend rdbms. Right now I’m working with Xampp on a local host but will eventually have this all hosted remotely on the 'Net.

I need a tutorial and/or example of how to take data scraped from an entry screen and add it to the database. If it makes any difference, I’m an old (83) mainframe programmer who is taking up web devolpment as a retirement hobby. I’ve been through enough HTML and CSS to be able to make my frontend (almost), but I am now looking to the backend. This will force me to choose and learn backend code (javascript or php, maybe) which I’ve started on.

Can anyone point me to a good online tutorial?