Hi Lawrence, "I am at work" means you are doing work at your place of work. English speakers use it as a shorter way of saying "I am currently working at the place where I work at." It lets the listener know that you are busy doing what you have to do at the place you have to be at. Am I confusing you? Please let me know if I am =) EDIT: @Jessica - Great minds think alike haha =D

You're right, it means you are currently at work and doing work. It's an easier to say "I am at my place of work right now." It implies you're at the place that you work and also that you're actively doing the work.

It can have two meanings. In one context it can mean "I am busy" You may see a sign that says "Warning: Men at Work" Which means builders are working nearby. In another context it can mean "I am at the place where I work."

Your sentence just means "you are working". You may or may not at your work place. "I am at work" = 我在工作