This document provides an introduction to using can and could to express abilities and possibilities in the past and present. It begins with definitions of can and could, explaining that can is used for present abilities while could is used for past abilities and possibilities. Examples are given like "I can swim" and "I could swim." The document then discusses forming questions with can and could and provides example sentences. Multiple exercises follow for the reader to practice using can and could in different contexts. Additional online resources are also referenced.