If you want to start a new line, click "Newline" button.
If you want to chat with someone in the same room privately, you may hit his (or her) nickname in the right roommates list and select private chat, then the private chat window will appear. The nickname of the user you chose will show at the taskbar below. How many private chat windows you open, then how many nicknames exist in a line below. The default max number of private chat windows is 5. Administrator can change it to be more.