I have absolutely no idea how to participate, I'm relatively new to the game and the Halloween one was much clearer.
i'm afraid Brew Day is over for this year. Bristlebane Day is not long off, though, starts March 28. I recommend perusing the EQ2 wiki site for helpful info; lots of good stuff there. The monthly Moonlight Enchantments is active right now if ya looking for something else to do. It's kind of like a mini 2-day holiday thingy that pops up monthly; it is over after tonight though, so check it out on wiki, see if it sounds like fun to you.
Click the EQ2 button, then Calendar. That will show you when festivals and holidays are occurring. All month long, the Chronoportal Phenomenon is ongoing, Moonlight Enchantments happens from 12:01AM on the 20th to 11:59PM on the 21st of every month (PST), and Bristlebane Day festivities are coming up. The first week of each month has a City Festival that rotates among the major cities. The holidays are: Erollisi Day Brew Day Chronoportal Phenomenon Bristlebane Day Oceansfull Festival Scorched Sky Celebration Tinkerfest Nights of the Dead Heroes' Festival Frostfell