A lot of newbies in the baking world often get confused when they see "confectioners' sugar" and "powdered sugar", but actually these two are the exact same thing!
Confectioners sugar and powdered sugar are terms that refer to the same type of sugar. Another name this type of sugar is icing sugar. Powdered sugar or confectioners sugar is made from finely ground granulated sugar with a small amount of cornstarch.
Do note that only a small amount of cornstarch is added to prevent excessive moisture and clumps in the powder.
These are commonly used for baking or for desserts such as frostings, glazes, or sugar dusting on top of cakes and doughnuts.
This type of sugar is also commonly used in mixtures, batters, and smooth sauces. This is because the finely ground sugar easily dissolves and can be incorporated quickly into liquids.
Powdered sugar can be found in any grocery or baking supplies store, however, you can always make your own if you find yourself in a pinch. Simply blend white granulated sugar until pulverized.
Although not necessary, it is a good idea to add 1 tablespoon of cornstarch to the powder to avoid clumping. Sift the powdered sugar with a strain before using it. This will help get rid of large granules and get rid of grainy textures.