Class means a group of students meeting regularly to study a subject under the guidance of a teacher or a period during which a group of students meets for instruction. example- today kelly is not going to attend the physics class. Lesson is an assignment or exercise in which something is to be learned in classes. example- this lesson is hard so you should pay attention more. A course/coursebook or textbook, a book designed to accompany a specific academic course, or one specified by the writers of the course to be read by its students. example- kelly is about to finish this chapter of English language coursebook.

A particular class is a subject session scheduled for a particular time and day for an amount of time. Class can sometimes be used in place of lesson, but Universities here now tend to use class in the sense that I have explained. A lesson is just one of those classes. A course is composed of many different classes. So reading and writing classes may be in a English course.

Course = onward movement. There are usually many lessons that make up a course. The lessons in a course are the building blocks that make someone ready to pass a final exam. Think of lessons as the little things that we learn along the way. A class basically means learning a classroom environment. "Did you go to class today? I thought you were taking that course in math."