In most cases, teeth are pulled because they're badly decayed or damaged by trauma and cannot be restored anymore. Other times, they may need to be pulled to prevent overcrowding or because a significant infection is present.
Not necessarily, but it's usually a good idea. First of all, wisdom teeth that come in crooked or sideways and those that are impacted (stuck under neighboring teeth and unable to erupt) should be removed to avoid crowding and other serious issues that can affect your entire mouth and overall oral health. But even if wisdom teeth come in straight, their location way in the back of the jaw makes it difficult to keep them clean, which means they're more prone to decay and infection, which in turn can spread to other teeth. They're also more likely to develop gum disease. Having these teeth pulled is a proactive step in maintaining better oral health.
That depends on where the tooth is located in your mouth and how badly it's been damaged. In a simple extraction, the nerves that provide sensation to the tooth are numbed to prevent pain, and the tooth is firmly grasped and pulled using a special instrument. But when a tooth is broken, cracked or otherwise damaged, an incision may be needed to remove the entire tooth, including the portion beneath the gum. Once the extraction is complete, you'll need to follow post-operative instructions to avoid infection and prevent dislodging the blood clot that forms in the initial stages of healing.