"Rules" is a noun that means principles or guidelines that are followed in order to achieve a particular purpose or standard. Here are some examples of how "rules" can be used in sentences:
Please follow the rules of this game.
Rules are made to be broken, but only very infrequently.
The rule of thumb is a simple way of doing things that includes all possible situations.
You should play by someone's rules, especially if you want to succeed in their environment.
The rule of law is important for maintaining a just and fair society.
In these examples, "rules" is used to describe the principles or guidelines that are followed in different situations, whether it's for playing a game, following someone's expectations, or upholding the rule of law.