The document discusses the use of can and can't to express ability in English. It provides examples of affirmative sentences using "can" with subjects and verbs, negative sentences using "can't", interrogative questions using "can" and short yes/no answers. Ability is expressed for common actions like speaking languages, taking photographs, swimming, dancing, singing, acting, flying and more. Questions are provided asking about ability followed by short answer responses of "yes, I/we/she/he/they can" or "no, I/we/she/he/they can't".