The document discusses the use of modal verbs such as can, must, might, should, may, will, and would. It provides examples of sentences using these modal verbs to express different meanings such as possibility, necessity, permission, and prohibition. For example, "He must be exhausted after such a long flight" uses must to express necessity, while "If you want to get a better feeling for how the city is laid out, you may walk downtown and explore the waterfront" uses may to indicate possibility or permission. The document also contains exercises analyzing the correct and incorrect uses of modal verbs in different contexts.