What you wanna do is quite simple. However , if you haven't done any php/mySQL it might get annoying.
In any case, it's a great project to learn php 😃 😃
The bare bones are here:
First you need to have a table in your db.
Call it Forms (or whatever else....)
You need at least two fields, ID, Comment.
Create an html page , with a form, and comment field, submit button.
Set the form action to display.php
create the php page, display.php.
Within that connect to the db, insert info, display info.
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Remember this is just the simplest method. There are more complex ways of doind it (like displaying and processing the form on one page....)
HTH