I don't know whether I can join the chatting room. Sometimes there're people chatting already, can I join them?

Is it very impolite?

Hi Zacharius,

Of course you can join the chat whenever you want. Everyone is welcome. Emotion: smile
how can I choose a chat room that suitable for me?
Students: Are you brave enough to let our tutors analyse your pronunciation?
Just choose any you like. You may want, however, to join a room with most people chatting at the moment.