when does pottermore start? how do i register? has it started?

It's projected to open in October, but this does not mean it automatically opens on October 1st; when they complete the Beta testing, they'll announce it. Hang in there. :)

Well they said October, but no one knows when exactly. The problem is that they don't know how the page will react to such a high demand (can you imagine millions of people trying to get in all at once, on October 1st?)
Even now the page occasionally crashes, and that's just when one bunch of welcome letters is sent out. I can't imagine how it's gonna be in October...
You just have to be patient, that's all.