What is PHP really used for not talking about forum pocketmine or any of that although what it was really made for I know it's a scripting language although I don't know what it means by that <?php
I might not be the best one to answer you but: PHP is by it's origins a Web scripting language processed server side (when you make a request to a website, the server where the website is located will process all the PHP code then output the content to the user). That's what PHP was meant to do. After a while, the PHP devs added a way to do OOP (Object Oriented Programming) and Phars (php archives). After that, some developers, like shogicp, the founder of Pocketmine, choosed PHP to create server side apps (your MCPE server's plugins are processed server side). The issue with PHP is that it's reeeaaaallly slow compared to other languages such as Java (Bukkit) or C# (MiNET). PocketMine plugin developers such as me or most of the people on those forums are using PHP to create plugins hich afects behaviors of the game. If you have any further questions, you can ask me.
<?php means that the code after that is PHP code. If you don't put them there, it will just consider it as a normal HTML document and output it directly.
I read somewhere that it was planned to be a template language (correct my sentence) but didn't went that way.
PHP is like JS in the way that it is dynamic. However, they are both different (syntax, functions). PHP is like Java and JavaScript into one. It can be used on web server AND on local