Hydration is simply the ratio between water and flour. A dough made of 500g of flour and 350g of water is 70% hydration.
Much of baking can be reduced to engineering values, but some aspect require more art than science. For example, the size of an egg is not always consistent, so a recipe that calls for an egg might require more or less flour to achieve the desired result - important for cookies and cakes.
Yeast is simply magic. It's in the air and everywhere. And certain strains will taste better than others. This perhaps matters more for beer than bread, but you get the gist. Fermentation can be somewhat unpredictable when you start out. But you'll find what works for you and tips from others help.
How much you should work the dough, how long you let it rest, and whether you cycle that process a second time, are not things easily conveyed in a recipe and can depend on feel and can be influenced by the temperature and humidity of your cooking environment. So a certain amount of trial and error is necessary... or perhaps in your verbiage - failure analysis testing.
