The document discusses the use of modal verbs to express permission, obligation, and prohibition. It begins with an example game using modal verbs worth various prize amounts. It then defines modal verbs as special types of auxiliary verbs that alter or complete the main verb's meaning and expresses ideas such as possibility, ability, obligation, and permission. Examples are provided of modal verbs expressing permission (can, could, may), obligation (must, have to), suggestion (should, ought to), and prohibition (cannot, must not). Activities are included for students to practice using modal verbs in sentences appropriately.