That green fungus growing on your bread is called mold — use it as a science experiment if you want to, but you definitely shouldn't plan on eating it. Mold grows where there is damp, decaying organic matter.
A mold is also a container that certain foods or materials — like gelatin, chocolate, wax or concrete — can be poured into. When the food or material sets, it will keep the shape of the mold. If you pour red and blue gelatin into molds shaped like stars, you'll have a great patriotic dessert for the Fourth of July. As a verb, mold can mean to influence. Good teachers mold their students' interests and passions.