Right side will show list of members who are present in that room.
Clicking a members names in the right side list will show the "user options" as shown in the image above and each option is explained below.
Mention Mention allows to mention a member in your message and it will appear highlighted to them.
Whisper After typing your message, selecting "whipser" option will send your message as a whisper.
View Profile This option only show for registered members and will take you to their profile page.