You go to the main page (the list of forums)
Beneath the list of forums you see "Currently Browsing the Boards (number)". Click on that, you'll see who's online
Don't worry, took me a while to figure it out too!
------------------
Sapphire Dragoness of ALSB
Waitress at Cloudy's Cafe
Guardian of the Temple of Aerie (specialized in GenCon and BG)
Most Illustrious Arch-Magess of the Illuminati
Lux omnis est