Marble Brownie Recipe How Would I 'marble' Brownies?

How would I 'marble' brownies? - marble brownie recipe

I am new in the oven and found a recipe for homemade brownies, which I seek. I want either a marble or white chocolate, add peanut butter, or drizzle on. Do I Melt chips, such as milk and sprinkle before cooking? I want to stay up, but I will not be difficult.
Thank you!