This document discusses stem-changing verbs in Spanish and describes the three types: Type 1 verbs change e to ie, Type 2 change e to i, and Type 3 change o to ue. It provides examples like entender and servir. These changes only occur in the present tense forms of the first, second, and third persons singular and plural. The document also discusses irregular verbs like tener, venir, and decir, and how verbs like querer and preferir can be used with infinitives to express desires and plans.