When you have a bad tooth that is pushing other teeth to the side, or a tooth that has such a bad cavity that it can't be fixed, you may to have the tooth taken out. This is called an extraction.
When you have a tooth pulled, the dentist gives you a special medicine called anesthetic. Once your mouth is numb, the tooth is taken out. This really doesn't hurt, since your mouth is numb. The most you will feel is probably some gentle tugging and wiggling.
When we get older, sometimes teenagers and young adults have to have their "wisdom teeth" pulled out. The wisdom teeth are the large teeth in the very back of your mouth, on both the top and bottom rows. Lots of people have problems with their wisdom teeth growing in the right way; often, wisdom teeth get stuck, or "impacted," and start pushing other teeth. To keep the other teeth from growing in crooked, or causing other problems, the wisdom teeth may need to be pulled.
Don't worry, we really get along just fine without our wisdom teeth.