Android. How to make an alert?

Question

Android

I am writing a program for one school on the phone.
I learned that you can write a site, and the program will open the site inside.
I need to make an alert say a day before the event. Let's say there is a lesson tomorrow, and we need to make sure that the program sends notifications the day before the lesson that some task needs to be done.

How to make such an alert on html (as spam sites sometimes send)? Will it work for phones?

Ps I want to do in android studio according to the tutorial
https://youtu.be/ASd5QsE46nk

Answer 1

And what about HTML when it comes to notifications in Android?
Android notifications , Create a Notification