A dancer is a person who dances. Some people are employed as dancers, which makes them professionals. The woman in the picture is a ballet dancer.
A dentist is someone who looks after other people's teeth. They clean your teeth properly, and fix up holes in people's teeth. They can also make your teeth look better by straightening or whitening them. Sometimes going to see the dentist can be painful or scarey, so if you don't want a dentist trip to be bad, you should look after your teeth and brush them every day.
Detectives are usually members of the police force. They investigate crimes, and try and work out who committed a crime and how.
A doctor is someone who makes sick or injured people better. Their main role is to find out what is wrong with someone and prescribe treatment, while a nurse's role is mainly to look after sick or injured people as they get better. Some doctors perform surgery, cutting people open to fix what is wrong inside, to help people get better.
A drover is someone who drives livestock like cows or sheep from place to place. Drovers usually ride horses or motorbikes.