This document provides rules for using c and z in Spanish orthography. It states that c and z make the same sound and can be confused. The rules are that c is used before a, o, and u, while z is used before other vowels. It also gives examples of how z is used with suffixes like -aza, -anza, and -eza. The document recommends immersive Spanish courses and resources like BBC Spanish, RAE dictionary, and Spanish Wikipedia as useful ways to learn Spanish beyond just learning the letter rules.