Why hello there, and welcome ^^
I'm Avaritia, but you can just call me Ava, or whatever sort of variation comes to your head. And in reply to your question, you do need to make a trainer, but you don't need to make a Pokemon. The Pokemon Creation is only if you ant some sort of new Pokemon to be available. Though you could create a custom Pokemon, have it approved, and then start with it, it isn't nessassary.
I hoped that answered your question, if not, then I'd be glad to clarify :3
Nice to meet you
-Avaritia~