Fold in Scade Suite is confusing me

So I know how the reduce, accumulator and how fold works in C++, Python, etc… But for some reason in Scade Suite it’s kinda confusing to me.

Scade Suite Example That is confusing me

What I’m not understanding from the example is are the two arrays multiplying with each other without the accumulator value? How are both arrays being stepped through, how are they being multiplied by each other and if that can happen what’s the point of having an accumulator value in the first place. Can someone break this down for me. I’m dumb.

Source: Windows Questions C++