How to make Wordpress plugins auto-activate?

Question

Programming

Good afternoon. After studying PHP, I started learning Wordpress for myself. Actually, for some time now I can’t understand one detail: how to ensure that plugins automatically work without any user action? As examples, I will give a couple of orders that I use as practical tasks:
1. There is a task "Send a reminder letter to the user 15 minutes after placing the order if he did not pay for the goods." How to start this timer for 15 minutes? After all, the page is most likely to be closed, all sorts of hidden counters in the code are useless.
2. Automatic parser. This question is relevant for almost any grabbers. There are news feeds or dynamic pages. The parser can study them and select the data we need, writing them to the database, I can do this. But how to make it do so without manually starting it? For example, every 5 minutes I checked the page for records, checked the last one with the last record in the database, if it matches, I waited again for 5 minutes. Or are there some alternative methods of verification?
I understand that it is these tasks that can be solved simply by using ready-made plugins. But I'm interested in the logic of the solution itself. If I misunderstand something or miss details, I will be grateful for an explanation.

Answer 1

I'm very far from PHP and Wordpress, but it looks like you need this