Don't know how I do login page with mysql database?

Hello, (sorry for my english iam not english) I have a project for class where i have to create an application for a school. Basically i have to create a login page first where i get my id and password in Mysql, the mysql is in a pc that we have in class and we use it as a server, im not really smart in this so i ask for u guys how to connect my application to mysql

See here:

https://puravidaapps.com/mysql.php

It doesn't help me i still don't understand a lot

which part you don't understand?