The document discusses English modal verbs including can/can't, could/couldn't, should/shouldn't, must/mustn't, and have to/don't have to. It covers the uses, structures (affirmative, negative, interrogative), and meanings of each modal verb such as expressing abilities, possibilities, obligations, prohibitions, advice, and permission. Key uses include can for abilities and possibilities, could for past abilities and possibilities, should for advice, must for obligations, and have to for necessity without other options.