Someone have a good website to learn php?

this
https://secure.php.net/manual/en/langref.php

also this is needed https://php.net/manual/en/language.oop5.php
and this https://php.net/manual/en/language.namespaces.php
these are the ones MOST sites wont teach you but it's necessary to make PMMP plugin
all others in the first link IS encouraged to be learnt
after all this learning you should be able to learn PMMP API by reading it's source code or parts of it to make your own plugins

 

because it mainly is but you can use it to do other stuff anyways,
like a wrench may be a tool to turn nuts, it still dosent meant you cant use it to smash glass bottles