Flour comes from the berry of the wheat grain. The wheat berry, or kernel, is composed of three parts:
White flour, the kind most commonly used for pizza dough, is made by grinding the endosperm into a fine powder. When the proteins found in flour are mixed with water you get gluten—a strong, stretchy substance.
The starches in the flour combine with the gluten to form a viscoelastic matrix that is the structure of your dough. This matrix traps gases from yeast fermentation which causes the dough to rise. Stronger dough made from high protein flour and longer mix times limit the rise and yield thinner, crispy crusts. Weaker dough made from low protein flour and shorter mix times will increase the rise creating thicker, softer crusts.
The starch in the flour provides enzymes and natural sugars for the yeast to assist in fermentation and aid in the browning of the crust in the oven.