What is the small green ball doing next to everyone's user name? Why is it red in some cases?

On the home page, if you hoover the cursor over the dot, a window will come up that lets you choose. I often put mine to red when I first log on to be able to answer messages first, or if I have a limited time, or long messages. There is also a yellow dot, which indicates they are logged in but away from computer.

Green is open profile, red means your profile isn't open to the public.

Green means online. That person is online right now.

It's the ep version of conversational traffic lights.

red means they want to left alone

thanks for ba