When it comes to making rules under Robert's Rules, one rule stands out: A group is free to adopt whatever rules it may want or need as long as the procedure for adopting them conforms to any rules already in place or to the general parliamentary law.
The reason for having rules in the first place is so that you and your fellow group members can mutually agree on governance (that is, who your leaders are, how you choose them, when you have your meetings, and so forth), procedures for arriving at group decisions, and policy covering the details of administration for your organization.
Different situations call for different types of rules. Robert's Rules classifies rules based generally on their application and use and on how difficult they are to change or suspend:
Charter: The charter may be either your articles of incorporation or a charter issued by a superior organization if your group is a unit of a larger organization. A corporate charter is amendable as provided by law or according to provisions in the document for amendment. A charter issued by a superior organization is amendable only by the issuing organization.
Bylaws: The bylaws are fundamental rules that define your organization. Bylaws are established in a single document of interrelated rules.
Rules of order: Rules of order are written rules of procedure for conducting meeting business in an orderly manner and the meeting-related duties of the officers. Because these rules are of a general nature about procedure rather than about the organization itself, it's customary for organizations to adopt a standard set of rules by adopting a parliamentary authority such as Robert's Rules.
Standing rules: These rules are related to the details of administration rather than parliamentary procedure. Motions your group adopts over the course of time related to policy and administration are collectively your standing rules.
Robert's Rules also mentions custom, referring to unwritten rules followed in actual practice. But because they're not written, they're not considered a "class" of rules.
