This document discusses using the modal verbs "can" and "can't" to express ability and permission in English. It provides examples of using "can" to say what someone is able to do, such as "My brother can play the piano." Examples also show using "can" and "can't" to ask for and give permission, like "Can I go to the toilet, please?" and "Yes, you can." Additionally, it notes that "can" is used to make requests, for instance "Can you close the door, please?"