From my perspective "necessary authority" is a meaningless phrase. Authority is always justified to those who support it, and unjustified to those suffering under it. For example, the authority of a particular country to enforce it's borders is "justified" in order to preserve those borders. The authority of a catholic priest is "necessary" to uphold the values of the church against sin and pollution of the faith. But if you don't believe in those institutions then the justification is very silly! Anarchists just take this one step further and realize there is no single true authorized power structure.
Anarchists can do away with authority and just act directly. If some of us agreed to live a certain way it's us deciding that we want to do that. We don't need to hit others over the head with a magic scroll or manifesto to prove we are justified, and we don't need to ask their permission first. Likewise, if someone wants to push us around we don't give them the benefit of the doubt through authority. They're just another person trying to push us around, whether they're a government agent or a highway bandit.
How you approach others is what makes your world the way it is. If you want to treat others as equals, directly, and engage with them without an intermediary we could say you're an anarchist. If you think you need government (an authority, legitimate justified power) to push others around, i'd say you're not.
the simple or flavorful use of 'authority' usually just means someone is well respected on a topic "She's an authority on electrical motors" or that they posses some leadership qualities and are well liked.
the second and more dictionary definition of authority is authorization to rule. literally to dominate others because they are seen as legitimate.
your example of a club is a good test ground for these differences. it's up to you to run your club, make agreements with other members and share responsibilities even if people are happy to let you decide things or do most of the work. but your club doesn't have any claim to legitimacy, to true authority, because it doesn't seek to control ALL activities of that type. in the case of government, it very much does claim authority over the entire nation, to determine who can move where, who can work where and how, who must fight and who must be put to death.
there's no competition allowed with a structure like government. either obey or resist and face consequences. i'd much prefer a world of overlapping autonomous 'clubs' whose members decide for themselves than a world divided up by the greediest and most violent mafias.