Download the Phar officially here
Take them and put them in your Virion folder. If you do not understand what Virion is, then click here
To implement and use methods, you must first use this library's method at the top of the plugin's onEnable function
Example:

protected function onEnable() : void
{
    VapmPMMP::init($this);
}

What is VapmPMMP::init($this) ?

/**
* @param PluginBase $plugin
*
* This method is called by VapmPMMP::init(), it will run event loop.
*/
public static function init(PluginBase $plugin) : void;

Finally, here's a guide to the methods you can use: here
This is plugin Example:
SimplifyLibasynql
VSharedData
VJesusBucket
VBasket
VOreSpawner