Creating a plugin

Start by creating the app/code/Foggyline/Plugged/registration.php file with partial content, as follows:

\Magento\Framework\Component\ComponentRegistrar::register(
    \Magento\Framework\Component\ComponentRegistrar::MODULE,
    'Foggyline_Plugged',
    __DIR__
);

Then, create the app/code/Foggyline/Plugged/etc/module.xml file with partial content, as follows:

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/ etc/module.xsd">
    <module name="Foggyline_Plugged" setup_version="1.0.0">
        <sequence>
            <module name="Magento_Catalog"/>
        </sequence>
    </module>
</config>

The preceding file is simply a new module declaration with the dependency set against the Magento_Catalog module, as we will be observing its class. We will not go into the details of module declaration right now...