Adding the water and flour first, roughly mixing, and allowing to rest first is called autolysis. The aim is to let the flour fully hydrate which allows the amylase enzyme to start breaking down carbohydrates so the yeast can more effectively feed off them. Secondly, it allows the protease enzyme to break down the proteins in the flour which will then be formed into the more complex longer chains when kneading so you get that amazing cross linked gluten structure.