That phrasing refers to a very broad set of movements and individuals. The usual core beliefs are:

• Legislation in their jurisdiction and the government’s authority to enforce it is in some way defective.
• People in their jurisdiction can opt out of laws and government, and live only under “natural law”.
• People have to perform a set of legal procedures (spells, effectively) in order to achieve that.

Exactly why and how law/government authority is defective, what natural law looks like, what the spells are that they have to cast - all of these are extremely variable both between jurisdictions and between individuals.
Primarily it’s a set of grifters charging money for courses and materials to learn about these beliefs from whoever they can convince. Sometimes as in Germany, it’s a group of neo-Nazis plotting to reinstate the Kaiser.

You might enjoy münecat’s longer form explanation.