Black tea is the fermented (oxidized) form of tea. First the tea is withered or dried over a low heat. Then it is rolled into a form similar to what you see in loose tea. Next and most importantly, the tea is fermented. This is really not fermentation in the traditional sense - instead it is oxidized in a slightly humid environrment. This is the key process that brings out the flavor of the tea. It is the tea maker's art to time this just right. Finally it is fired at a higher temperature to fix the flavor of the tea before being sorted into different leaf quality and sizes.

Black tea contains caffeine but much less than coffee - about 40 mg per cup, depending on strengh and steep time. (Coffee, by comparison, has 80 - 100 mg.)