Yeah I'm new to this culinary world and was wondering if whole wheat flour can totally replace white flour?
I've made some yummies brownies with all-purpose flour last week and they tasted good. If I do it again with whole wheat will it taste almost the same? Or is it a complete different story?

They are completely different. It will alternate taste and texture. What you can do it start by replacing only half of the white flour by whole wheat and see how it turns out.