He/she can save your perfect smile and save you from tooth decay (with help on your part) with their excellent skill and art form. Going at the recommended appointments can save you from pain later in life hopefully.
A dentist's job is to perform dental procedures. Procedures that involve the teeth. Some examples are an extraction where the tooth is removed manually, a filling where a cavity in your tooth is filled with a substance to stop it and cover it up, an implant where the dentist implants a fake tooth to replace one which you lost (only performed on adult teeth). Dentists also perform treatments for gum diseases like gingivitis.
Do not confuse a dentist with an orthodontist. Dentists only perform procedures on the teeth and gums not the position of the entire jaw in general.
Does that answer your question? I'm pretty sure you could have found this on google in seconds. What's up with that?