Google a bit, check out on the forums of sauerbraten.org (I'm very sure that question has been asked thousand times already) or check the FAQ of Sauerbraten...

I'm sorry but I don't have the knowledge about that any more since it's like a one-time during period. After you managed to create a server, you just stick to that one anyways (at least I did :P).

I do not understand what you are asking.

Not sure I understand your question exactly.. but..

It is just a that all servers must support Auth along side the regular master modes. A person can set a server to Auth only, which will disallow people from taking master unless they have an Authentication key, or the Admin password for that specific server. Or the server can set to the regular 'Open' setting, but Auth must still remain functional.

Servers that do not support Auth run the risk of being banned from the master server.
Auth is a way of maintaining a friendly environment by allowing trusted people to take 'master'
For example, if you've ever been on servers that run Venice all the time where nobody can take master, sometimes you will get a player who kills their own team, or is simply rude and extremely offensive. Somebody with Auth could take master and remove the offending player, they can also override a regular master should the need arise, such as a case where somebody who's taken master has started kicking people without rhyme or reason.