The document discusses the uses of the modal verb "can" and its negative form "can't". It explains that "can" expresses ability, such as "My brother can play the piano". It also uses "can" and "can't" to ask for and give permission, like "Can I go to the toilet, please?". Additionally, "can" is used to make requests, for example "Can you close the door, please?". The document provides examples for each use and instructs readers to practice the sentences aloud.