Hello! I am new at PHP (and the API of Pocketmine). I asked a few 'professional' Plugin Developer where to start with Pocketmine. Most of them told me to take an existing Plugin, reading it and trying to understand it. But there I don't know with which Plugin I should start. So I used Google and asked Google if there is a Tutorial for learning developing Pocketmine Plugins. I found just 1 tutorial on (GitHub) what looked in a way usefull, but it seemed to be outdated (created about 1-2 years ago) Now I'm here and I ask if there are any tutorials to learn it. Maybe suggest reading a Plugin that contains the basics of Pocketmine API (and in best case of PHP)
First learn basics of PHP and OOP (Object Oriented Programming) and learning PocketMine API is just practice and a lot of it. That's it.
I'm not a "professional plugin developer" but I don't recommend jumping right into the development. To easily understand the API, you need to learn PHP. First, learn the basics; variables, functions, arrays, strings, loops, if/switch statements, etc. Next, OOP, which are objects that can contain constructors, properties, constants, functions that run using the basics and/or other objects, and getter/setter functions. After this, you will be able to understand plugin code and learn about the api, thinking of something you want to create and turning it into code will be fairly easy and will get easier as you gain experience. Good luck. Feel feel to ask questions.