Browse around. Post.
Tripcodes are kind of like passwords- they are used to identify you. You should pick one and stick to it - that way, everyone will know it's really you, and not an imposter, and you'll also be able to delete and modify posts.
It doesn't really have any docs written up yet, so clicky-clicky around. And don't use IE, because it sucks and doesn't work right. And that's not just here, that's just a general thing.