Wikipedia:Policies and guidelines describes how Wikipedia arrives at its policies and guidelines through a process of discussion and consensus. Discussion takes place in the mailing lists and in the various policy pages which form part of the "Wikipedia:" namespace.
Two words for the same thing. An administrator is simply a Wikipedian who can access the few restricted Wikipedia software functions: deleting articles and uploaded files, protecting and unprotecting pages, and blocking and unblocking IP addresses. The software internally uses the string "sysop" to flag their accounts, perhaps one reason that term is used. They tend to be friendly folks that are willing to help you, if you post on their "talk page". See the current list of administrators.