If a tooth has been broken or damaged by decay, your dentist will try to fix it with a filling, crown or other treatment.  Sometimes though, there is too much damage for the tooth to be repaired.  This is the most common reason for extracting a tooth.  Extractions may also be performed for orthodontic reasons.  People getting braces may need teeth extracted to create room for the teeth that are being moved into place.
A simple tooth extraction is the removal of a tooth from its socket in the bone without complications.  This procedure is performed on a tooth that can be seen in the mouth.  Most of these can be performed by using just an injection (a local anesthetic).  In a simple extraction, the doctor will grasp the tooth with a forcep and loosen it by moving the forcep back and forth.