Chats are run by other members of the site, sometimes they cannot run the chat and announcement will be placed in Chat Annoucements thread. Sometimes an announcement is not made, it all depends on what is going on with the person who is running the chat.

transientsoul: to access the other rooms, there is a "door" like button next to three other buttons. Click on that button and a list of rooms pops up. Choose the room you want and click on it.

I hope this helps.