The Cahn-Ingold-Prelog priority rules are a set of guidelines used to determine the priority of substituents attached to a chiral center in a molecule. These rules help chemists assign the correct configuration of stereoisomers, which are molecules that have the same molecular formula but differ in spatial arrangement. To apply these rules, substituents are ranked based on atomic number; higher atomic numbers receive higher priority. If two substituents have the same atomic number, the next atoms in the chain are considered until a difference is found. This systematic approach is essential for understanding molecular chirality and reactivity.