Most of them are volunteer positions once appointed by the big guy Brian the founder or one of his designatees appoints these roles. They are appointed by the administrators by your posts and reputaion on the board. Some of the ones that say contributor are related to the number of posts if you are a subscriber. I hope that helps. YOu can look at the terms of service and upgrade your membership...it explains it better.
It depends on what you want it for. All that can be compared if you go to your account and go to upgrade membership. I like having my avatar of my dog and I like giving Brian his due for founding this site and keeping it updated and upgraded.
A more personal relationship with other members and more private. Of course if you are staff noderator and guide you obviously have different privileges and perks....I just don't know what they are....you can PM any one of them....
There is an extra forum for premium members that is private and you can also do classifieds if you want to sell or buy stuff. I was premium or platinum (don't remember them now) before I was asked to be on staff. I didn't even know exactly what the extra perks were. I just wanted to help donate to the site because I know how much costs and time goes into running a very very small site, let alone one of this magnitude. This forum helped me so much as a pre-nursing student and a nursing student that it was my way of giving back. I know there was the avatar, more private messaging, the ability to edit posts.
As staff there aren't any extra perks, it's a volunteer basis. Well it's not thankless, I guess I didn't word that right. They are very appreciative of the help. There is a link that explains the AN Guide. I will find it and post it. I think they get free premium membership and they also help with reporting posts and giving guidance and advice to other members.
If you find this site helpful and are able to afford it, I would definitely upgrade membership. You also get free of ads which I never realized how nice that was because I always paid for premium membership since I finally joined and stopped lurking. Well the other day I logged on from somewhere new but at first I forgot I wasn't logged on. I realized when I was thinking "where the heck did all these annoying ads come from" lol