This document discusses the modal verbs "can" and "can't" which are used to show ability or inability to do something. It provides examples of affirmative sentences using "can" to show ability, negative sentences using "can't" or "cannot" to show inability, and question sentences using "can" or "can't" with responses of "yes" or "no" to confirm or deny ability. It also notes that question words can be placed before "can" in questions.