What is the rule of each ingredients flour fat yeast and sugar?

Flour is the main ingredient, fat is used to help bind the flour grains together. A little warm water, and sugar is added to feed the yeast, which is then added to the flour. The yeast (balm) feeds on the sugar and multiplies, giving off carbon dioxide (and a little alcohol - which is destroyed on cooking). Th carbon dioxide causes the kneaded bread dough to rise and become lighter as it fills with gas bubbles. Once the dough has risen, it can be baked in an oven.