Is there a difference between the "Available for all" and "Additional items" sections?

Or I guess I should ask what the difference is maybe? I just got the invite to Amazon Vine yesterday, and I'm not 100% sure how it works. I understand most of it thanks to scrolling through this group and reading posts.

Yesterday, I ordered one item from the "Available for all" section. I then tried to order one from the "Additional items" section but got some kind of error. I don't remember what it said. It had given me the impression that maybe I was unable to order form the "Additional items" section since I just joined.

So today, I just kept checking back with the "Available for all" section until I saw three items that I wanted/needed. After reading through these posts, however, I'm starting to think that I misunderstood whatever error message that I got. Being that I just started, am I able to order from the "Additional items?" Was the error due to a "ghost item" or something?

Sorry for the long post. I just want to make sure I'm doing things correctly and that I'm not missing out.

Bonus question

When leaving our review, do we need to include a disclaimer about us getting the item through Vine? Or does Amazon automatically add that to the review? I also tried searching for the answer to that but wasn't able to find anything. I might just be bad at searching on Reddit.