Always use a comma when directly addressing someone or something.
Study these sentences:
- Ladies and gentlemen, may I have your attention.
(direct address/Ladies and gentlemen) - People in zone one, please queue here.
(direct address/ People in zone one) - It was a pleasure to meet you, Elvira.
(direct address/Elvira) - Please, children, be sure to wipe your feet.
(direct address/children)
