Your online status:
Online status makes you visible to all online users. You can send and receive online messages and you can start/accept direct chat with other online members as well.
Busy Status makes you visible to all online users as "busy". You can send and receive online messages , however other members cannot ask you for direct chat.. Only you can invite other members (with online status) for chat. Change to this status if you just want to browse profiles or check messages but don't want to chat with other users.
Offline status makes you appear offline. You will not be shown in the "who's online" search. And you will not be able to ask/accept direct chat from other members as well. Change to this status if you just want to check messages or view other profiles.
You can toggle between these status while online. You can also choose to always appear offline when you log in. You can do that by changing your settings from the " Your settings" in the "Your profile" menu.