If you have a broken tooth, see a dentist right away. Broken teeth are usually caused by an injury. A broken, or chipped tooth can be more sensitive to heat, and cold, so even if you don't think it's the damage is extreme, you should let a dentist give you a thorough examine first.
If the tooth is chipped, it can be repaired with dental bonding, enamel shaping for smaller chips, or veneers for larger ones generally on the front teeth. If the tooth's broken, try and collect any pieces, and place them in a sealed container with milk or a saline solution. Be sure to treat any bleeding areas with gauze, and rinse out your mouth with water. Broken teeth may only need a filling to be repaired if the break is only in the outer enamel, or if it has gone down to the dentin. A crown can also be used. If the nerve is damaged, you may need a root canal.