Not complicated at all. Normally there's a period where people nominate fandoms. Those fandoms get stuck on the official list and then, when you sign up for real, you select 3-4 that you want to receive and as many as possible that you'd be willing to write for. (You only end up writing 1 and receiving 1.)

Announcements are on the lj community. Actual signups and nominations are on the website. You can still see the unfilled requests from last year up on the website.