they're referring to your bitcointalk member rank. you can't enroll while you're a newbie.
you should know this if you read their signature campaign thread.
I have no idea about the second question.
thanx.can you explain when my rank will be changed?
https://bitcointalk.org/index.php?topic=178608.0you will become Jr. Member when you reach 30 activity. you can increase your activity by posting, but it will only increase by max of 14 for every 2-weeks periods you posted in.
if you have more question about activity (not about yobit), ask it on that thread I linked.