What is Potato Flour?
Potato flour is ground or "milled" from the whole potato which is cooked then dehydrated. Potato flour absorbs large amounts of water,and cannot be the main flour for baking, your  recipe will turn out gummy.
Potatoe flour is used as a thickener in soups, gravies, and sauces.
Potato flour is more heavy than wheat flour and has a definite potato flavor.
Small amounts are used to increase water and help hold together a recipe, it is  mixed with other types of flour for baking.
For general baking substitute up to a 1/4 of the flour in your recipe with poiato flour.
For yeast bread recipies you can substitute up to 1/6 of the flour with potato flour.
A few Tablespoons of potato flour added to a recipe will add moistness although too much will make it more "heavy" or dence.