Pizza, bread, pie, cakes, cookies. They all start with flour (well, there are a few exceptions). You can make flour from many grains, seeds, beans, and even roots. The most common flour is made from wheat, but there is also rye, rice, corn, buckwheat, chickpeas, potatoes, and even hemp seed!
Sometimes oils must first be extracted, the outer husks removed, the inner germs separated, and then the the grains/seeds/whatever are dried and smashed in a process called milling. Sometimes they are bleached. Because flour contains oils that can go rancid, flours should not be stored at room temp for longer than four months. Some people store it in the fridge, but that is not necessary. It should be stored in an airtight container. It attracts a small pest called the pantry moth.
I strongly recommend that you use a digital scale to measure flour. There can be a lot of air in flour and a cup or other volumetric measure can vary significantly depending on how the flour is ground and how tightly packed the cup is. But when it comes to weight, a pound is a pound the world around.
Wheat flour is the type we use most often for pizza, breads, and pie crusts. It is a powder that is high in carbohydrates, protein (called gluten), amino acids, oil, vitamins, and minerals. There are different types of wheat flours in the size of grains and the percentage of protein.
Whole Wheat Flour. Made from the whole kernel with the bran, endosperm, and germ. It is tan in color.
All Purpose Flour (APF). A bleached white powder made from the endosperm of the wheat. There is no urgent need to stock any other flour than APF. Pizza fanatics have become a bit weird about their flour choices, matching them to oven temps, using bread flour at lower temps, APF for medium temps, and 00 (double ought) for higher temps. I find that all purpose flour (APF) works fine, no extra inventory necessary.
Bread Flour. A bleached white flour that is higher in protein.
Cake Flour. A bleached white flour, this has the lowest gluten content of wheat flours so it is used for light products like sponge cake.
Gluten Free Flour. A blend of non-wheat starches such as rice flour, tapioca starch, and potato starch.