Sugar is essential for most baking recipes. In order to have good results, there are a few things to keep in mind.
White Sugar is the most commonly used type. You want to get it finely granulated – this is the ordinary way it comes. Lately, there have been more and
more coarsely granulated types available. These are useful for some recipes, but will reke havoc with most baking recipes.
Brown Sugar is White Sugar with Mollassas added. (This does NOT mean you can just add mollassas to white sugar if you are out. I tried it a few times and they were all awful.) You probably want Light Brown sugar as that is what most recipes mean unless they specifically call for Dark Brown. Look for a bag without those little hard dark lumps – they can be really hard to get out.
For both White and Brown sugar you want to purchase Pure Cane Sugar if at all possible. Beet sugar is being used more and more and often creates problems with taste and texture in baked goods.
Powdered sugar is most often used for frosting and candy. It will probably say something like 10x powdered. It is often also referred to as Confectioners Sugar.