Chat Within Email
In my opinion, chat and email are two separate applications, but Google didn't ask for my opinion. Within Apps Mail you can fire up chat sessions with any of your clients. You can chat, save chat sessions, respond later to messages, and even add voice and video to the service.
For your Apps Mail exam you'll need to know how to configure chat, start and end a chat session, and even turn off chat. There are some other features like chat notifications and links within chat that you may need to explore to for your exam.