Just as the title states... Does Pocketmine support addons? And if yes, could someone please explain how?
No, Pocketmine does not support add-ons. Add-ons can only be used in singleplayer, Xbox multiplier, Realms, and the official server software. No third-party programs will work with them, and that includes PMMP. PocketMine does have it's only plugins, but if you must use add-ons I'd recommend using the official software. You can obtain it for free from here: https://www.minecraft.net/en-us/download/server/bedrock/
but hey, does the official minecraft be server will work on any pmmp plugins? i mean is the pmmp plugins compatible with that official one?
Nope. You're gonna have to choose between Pockmine plugins, or add-ons and vanilla features I'm afraid.
Add-on has 4 parts. Resource pack (Pmmp only supports this) Behavior pack Skin pack Persona pack (Private / Not sure / Pmmp doesn't support this)