AbstractFactory method in DesignPattern

I am going through AbstractFactory DesignPattern in tutorialpoints site(http://ift.tt/1wDERKg). I understood the basic concept. I have two doubts here.

1. I didnt get the use of AbstractFactory class there. What advantage we got when the Factories are of AbstractFactory type.

2.moreover why to use class there? we can go for an Interface right?

Thanks in advance :)