Adding functionality to a superclass function

Hello World!

I just made my jump into OOP and I am quite excited to find out such marvelous things that I did not know.

If someone has a quick answer or can point me in some direction please reply to this question:

How can I, if at all possible, modify a function from a superclass but preserving all of it’s functionality? I know about the “override public function” but that is not precisely what I want.

Thank you!