the basic differences in commercially-available flours have to do with their protein content, and the protein content greatly affects the texture of the four and how suitable it is for certain applocations:

bread flour---milled from hard wheat, has a very high protein content. not suitable for delicate pastries and cakes. widely available in specially marked bags.

all-purpose flour---combination of about 80% hard wheat and 20% soft wheat. can be used for all types of baking.

whole wheat---milled from whole grains, must be stored in the fridge as oild from the germ & bran can cause it to go rancid. widely available, but buy only as much as you can use so it stays fresh.

pastry flour---milled from soft wheat, protein content of about 8%. unsuitable for breadmaking as it can hold a lot of fat. this, however, makes it terrific for pastry and rich cakes. i have only seen this available in bulk at our local co-ops and whole foods markets.

cake flour---finer still, at about 6% protein. ideal for all cakes, especially those that depend on physical leavening (angel food for example). usually sold in boxes in your baking supplies area of the store (Softasilk is one brand name).

hope this helps!