What are you waiting for? Run to the nearest emergency room or would you rather get tetanus, blood poisioning and possibly face amputation of your foot, possibly your leg?
Lesions on the bottom of the foot call for urgent care because the circulation to feet can be dicy and the area is used for all kinds of jobs that can put bacteria into the wound and cause infection. Extra care for cleaning, an updated tetanus shot, and other care is needed.
You should get your foot checked by a doctor. The nail may be dirty and may have bacteria. So keep your heel clean by washing it and keeping it covered.
If you stepped on a nail, then you probably have tetanus. If you have gotten an infection in your foot, then you should get a tetanus shot immediately. Otherwise, the infection could spread and cost you your foot.