What does "I'm at your service" mean? and under what circumstances can it be used?

Native speaker’s answer
Rebecca
"I'm at your service" means that you're available or ready for use or to assist someone. You can introduce yourself and say it to indicate that you'll be available to help them with whatever they need. This can be used if you're paying for a service, or if someone offers their assistance, or as a polite introduction. As an introduction it either implies that the person is being paid to help out, they have a keen interest in you, or they're being dramatic. Ex: Welcome to the BNB! If you need anything, let me know. I'm at your service. Ex: Chris, at your service. => Dramatic introduction Ex: I'm Jim, the plumber, and I'm at your service.