Teeth are used for eating with and can also be used for protection. Some animals have teeth that are made to chew on animal flesh while other animals have teeth that are made for chewing on plants. Some creatures don't have teeth at all.
Adult humans normally have 32 teeth. Humans have baby teeth that fall out as children grow, and are replaced by adult teeth. Sugar does damage to teeth, although this can be prevented by brushing one's teeth after consuming sugar.