When you get a package of yeast it is dry. Since yeast is a living organism, it needs to be brought out of the suspended state that it is in when you buy it. There are directions on the packaging that tells you how to add it to some water and get it going again before you use it. If you fail to follow those directions, much of the yeast will never really become active living organisms again. You will see what I mean if you buy some "dry active yeast".