Generally if you live in a liberal state, you gain certain rights as a citizen including, theoretically at least, some degree of say over government through voting and access to your local member or congressman, law and order through a police force, access to a lot of government provided infrastructure like roads, bridges, parks etc and basically a right to be a member of society. With that comes responsibilities like paying your share of taxes, accepting the results of fair elections even if they do not go your preferred way and obeying laws even if you disagree,
There are restrictions on who counts as a citizen in a liberal state. You are not a citizen if you are still a minor, if you are in jail, you are an illegal immigrant or if you are mentally ill to the point of being committed to an institution to name just a few examples.
The modern day pseudo-anarchist trend for people declare themselves "sovereign citizens" and hence NOT a citizen of their country, has dubious legal status. It also seems driven in most cases by self interest and the desire to take all the benefits of a modern society whilst declaring laws, taxes and other obligations normal people incur as part of being a functioning member of a society do not apply to them, they can do as they please. Of course in doing so they rely on other people obeying the same laws they reject and not burning their house down, kidnapping their daughters and throwing them off a bridge.