Instant and Active Dry Yeast
I always use instant yeast when making dough. It's easy to use because 1) it can be added directly to the flour, 2) it doesn't need to be proofed first, and 3) cool water can be used when a slow rise is desired. In Active Dry Yeast, the granules are coated with tiny layers of dead yeast cells, so in order to activate the living yeast with sugar or flour, the coating must be dissolved in warm water. This dead coating makes up 25% of the yeast's weight, so if using Active Dry Yeast, increase the yeast used in the recipe by about ¼. It doesn't need to be exact, so eyeballing the amount is fine. If using Active Dry Yeast rather than instant, begin by dissolving the yeast with a little sugar or flour (this feeds the yeast) in a small amount of the liquid from the recipe (which should be between 100°F and 110°F). Let the mixture stand for 5 - 10 minutes until foamy, then add it to the remaining ingredients.