Class can mean a group of students in a school, who always attend the same classes and courses. Class can also mean a lesson like a mathlesson or a lesson for history. The two words can also be synonyms. It depends on the context. Course is a long periode of lessons, for example a course for german language can take even 2 months. Class as a group of people: The whole class was listening. Lesson: Today's mathlesson was boring. Course: I'd like to learn english so I decided to take an english course.

Class: A group of students meeting regularly to study a subject under the guidance of a teacher. Lesson: A part of a book, an exercise, etc., that is assigned to a student for study. Course: A systematized or prescribed series, a program of instruction. Class：通常指上课的班级，当指去上“课”，是指人员相对固定的情况。 The class had arrived on time for the lecture. Lesson：是一节课的“课”，一般是书的一个部分或章节。 The lesson for today is on page 22. He worked assiduously at his music lesson Course：一个系列的课程，比如某些等级考试，往往要通过几门不同的课程组成一个系列的课程，这时用course相对适合。 A course of lectures; A course of medical treatments.

lesson: 课， lessons in your textbook， 请看第一课(lesson1)，第二课(lesson2)...... class: 班， group in the same classroom , 这是我的班。 course:课程，emphasize a studying period, including many lessons , 我选了一年的汉语课程。

Lesson - 课，比如第几课了之类的 class - 课堂 course - 课程

Lesson - 课 class - 课 也有别的意思 course - 课程