It can load plugins packaged in .jar by looking in the manifest file to find information. You can take a look to the PluginLoader testplugin repository to find how plugins are made.

The PluginManager object is a singleton, so you can access it using

PluginManager.getInstance();

You can set if you want to use logs using this line. It will create a log folder and save logs as zip files.

PluginManager.getInstance().setUseLogFile(true);

You can then load plugins using

PluginManager.getInstance().loadPlugins(new File("plugins/"));

It will load all plugins in the specified folder and call their onLoad() method. If you just want to load one plugin, you can also use

PluginManager.getInstance().loadPlugin(new File("plugins/myPlugin.jar"));

At the end you must use this static method

PluginManager.close();

It will call the onUnload() then unload the plugins and destroy the PluginManager instance.

So, in your plugin main you should have

PluginManager.getInstance().setUseLogFile(true);
PluginManager.getInstance().loadPlugins(new File("plugins/"));
PluginManager.close();