I thought I explained earlier in the thread but can go into a little more detail.
Potato starch is fine like corn or tapioca starch. It has the same properties so will thicken liquids when cooked and can be combined with heavier rice flour to make a gluten-free all purpose flour mix (mine is rice flour, tapioca starch and potato starch in a 3/1/1 ratio).
Potato flour is more the consistency of ground potato flakes. It is a little heavier and can absorb liquid without being cooked (like flour, but can not be used as flour alone because it absorbs too much).
Here's a link that may help The Food Allergy Queen: Potato starch vs. potato flour