The word do , along with does and did , appears in many English sentences. Why? Well, the answer is usually a mystery to many ESL/EFL students; it’s usually a mystery to more than a few ESL/EFL teachers too. But believe it or not, it doesn’t have to be a mystery. Why not? Because there’s a rule for using do , and the rule is rather simple once you understand a few things about English grammar. In this short, readable guide written by a former ESL teacher, students and teachers will learn the rule for using do , see lots of examples, and wind up conquering their fear of English’s dreaded do .