Hey, read the first three posts, it should help to clear things up a bit
Basically, when you sign up, you are given 750 BP or Battle Points. BP lets you buy Pokemon to use (you can't use any Pokemon otherwise). The cost of each Pokemon is determined through viability rankings, price list is on the second post of this thread (page 1). Every 2 days you get BP allowance, and this can be raised by buying Pokemon (each Pokemon raises your allowance by a bit, see price list) or laddering under your BC alt. A place in top 100 on NU ladder gives you extra BP, but you can only use your Pokemon that you have. Also, you can challenge other people in the challenge to win or lose BP. When you're ready you can challenge the Castle Head (FLCL) to finish the challenge but if you lose, he can take something from you.
And yeah 30 BP to Metal Sonic