Do you have an event or contest going on that you want people to know about? Tell them about it here!
When you post in this forum, you can set a start and end date for your event. People checking the forum will see what's coming up and when, and you can post with updates as the event draws near (or goes on). If you only need to set one date, that's fine.
To choose a date, click in the From and To boxes when adding (or editing) a post. You'll see a popup asking you to set the date and time. This is in your time zone; the display will be adjusted for users in other time zones.
Here's a handy reference (not accounting for daylight savings time when it applies) for some common time zones:
GMT (UK, Portugal)
CEST (Much of western Europe): GMT + 1
EST (Eastern US, Brazil): GMT - 5
CST (Central US): GMT - 6
MST (US Mountain): GMT - 7
PST (US Pacific, BYOND Standard): GMT - 8
Australian time zones: GMT + 8 to GMT + 10
Obviously this is not an exhaustive list, but it should serve as a rough guide for when to expect the most users to be able to get involved.