Did I break a bone in my foot? Yesterday I fell walking up the stairs...Horrible pains through the top of my foot and instant swelling and bruising

Possibly. While trauma can certainly lead to a fracture, the foot/ankle is a very common site for sprains/strains. If you are unable to bear weight on that foot for more than a few steps or if ther is tenderness to touch a particular point such as the bridge of the foot or the base of the small toe, i would x-ray it to be sure. You can try icing and elevating the foot to see if there is any relief.

Get xray. Common frx of base of fifth metatarsal jones frx dancers's or ligament strain see pcp or orthopedist.