When you take a step, your foot typically hits the ground heel first and rolls toward your toes, flattening the arch slightly. As you push off the ball of your foot, your arch springs back and does not touch the ground. That's how normal feet are supposed to work. Unfortunately, many feet aren't normal.
If your foot rolls too much toward the inside, it's called over-pronation. This leads to arch strain and pain on the inside of the knee. If your foot rolls too much to the outside, that's under-pronation, and you're more susceptible to ankle sprains and stress fractures. You can remedy foot pain by compensating for these tendencies, but first you need to determine which way your feet roll.
Try the watermark test
Put your feet into a bucket of water, then make footprints on a piece of brown paper. What do your footprints tell you?
If your footprint looks like an oblong pancake with toes, you pronate excessively or have flat feet. Try molded-leather arch supports, such as Dr. Scholl's, off the pharmacy shelf. And when shopping for athletic shoes, ask a sales clerk for styles with "control" features, soles designed to halt that rolling-in motion. If arch supports or sports shoes don't help, see a foot specialist about custom-molded orthotic shoe inserts.
If there's little or no connection in your footprint between the front part of the foot and the heel, you under-pronate or have a high arch. This means a lot of your weight is landing on the outside edge of your foot. Ask for "stability" athletic shoes, which are built with extra cushioning to remedy this problem. And if you are prone to ankle sprains, wear high-top athletic shoes that cover the foot and ankle snugly to minimize damage from twists.