That's how extension works and its a way inherit the parent action and also way to register your custom actions. You don't need to find that parent id, just need to remember and use it. Once you deploy your changes, Spring IOC container takes care of it.
The second part is to enable or disable an action to either display under Folder Rules. By default they are enabled so if you are creating an action, and your intention is to keep the defaults then that particular property is not needed to be mentioned as you can see in first case, in second case action must be disabled so it doesn't show under Manage Rules and hence the property must be overridden to set the value to false.
you seems to be missing to read the instructions in the tutorial, it's already mentioned about the public action there. Quoting "Setting the publicAction property to false hides these actions from the action dropdowns. There's no real reason to do that, in this case—it's just an example".