If you're talking about general introduction to the site, the board descriptions for a start - fan stuff, gaming, fiction, music, art and so on.
You can bump old threads, but see if there isn't already an active thread - like in the last two weeks - on a particular topic before you start one of your own. If there's Touhou related questions you have, again, the board descriptions can help you there, and then take a look at the threads to see if there's a subject that might already pertain to your question. The
Touhou Addict Recovery Center has a Miscellaneous Questions thread, as does the gaming board,
Help Me Eirin.
Most of all, don't be shy about just participating. These are all friendly welcoming folks, and the staff will be more than happy to help you.