I dont understand the chat plugin

Hi

I have tried to ask this question before but no answer

I cant get chatplugin to work as I want.

Questions

1. Is i possible to use it only on a subsite on multisite
2. Can it be used as a chat beween a teacher and a student on a subsite
3. Do users of the chat need to be logged in and have a user on the subsite to be able to chat.

regards Hubbe