Yeast 101: Active Dry Yeast, Instant Yeast, Baking Soda, Baking Powder. Differences and Info
Note:  I am only putting this as an answer because it is too much for a comment and because the titles show.

Many of these topics are already covered:

Why use yeast instead of baking powder?

Why are there no recipes combining both yeast and baking powder?

Does active dry yeast really expire?

How to convert a recipe calling for active dry yeast into rapid rise yeast?

Is there any difference between bakers yeast and regular yeast?

Does active dry yeast really need proofing?

Can active dry yeast be substituted for a compressed yeast cake in baking?

Is &#39;Pizza yeast&#39; any different than normal baking yeast?

Can/should I use rapid rise yeast for longer proofing?