What are the bullets for?

You gain them by posting and making threads, also by referring people to the forum and have them type in your name when they register. They're the forum currency, just like they're the currency in the game. In the past, we've had some contests and prizes in which we used the bullets. The previous owner of this forum also had Microsoft points that he'd exchange for a certain ammount of bullets, but he's not the owner anymore, as you might've figured.

Now they're only used for name-changing and adding custom titles under your name. At the moment you're "Level 6 New Recruit", and will automatically be gaining in level as you post. I believe the ranking system is posted in some thread somwhere in News & Announcements.
For information about the namechanging and custom titles, you can check one of those two top threads in Suggestions & Concerns. For more info about bullets, you can check out The Market, at the bottom of the forum

 

Or you could do what i did and rob everyone