What is the difference between taking courses, classes or lessons?

Notwithstanding the fact that people will be sloppy with their language and use these terms synonymously:

Course is the broadest term for the study of a subject. It could be used to refer to an entire degree program, but it is most appropriately applied to a specific subject such as First Year English Literature.

Class is more specific and is most properly applied to a section of a course taught by one instructor to one group of students at a certain scheduled time.

Lesson is the most specific and implies a particular unit of instruction, such as would be delivered by a particular instructor to a particular class on a given day.

Each word paints a different image through association in the reader's mind. Here are some meanings associated with each:

• course - field of study, duration as in "time elapsed", the process of evaluation and grading
• class - teacher-student interaction, where the interaction does not necessarily include the evaluation and grading grading process
• lesson - a unit of knowledge, tutorial, achieving a greater level of understanding

Course is at the highest, most abstract (macro) level. Lesson is at the most specific, micro level. Both course and lesson are independent of time. Both are dependent on goals. Class is the least abstract, most tangible of the three. It is dependent on time. It is a process level word.

You know what image you want to convey to the reader. It may not matter which country the reader hails from. What will matter is the other words in the sentence.

When we want to talk about a period of time when we are taught something, we say we have a lesson. For the same occasion, especially as part of a group, we can use the term class: We have a History lesson/class at nine.

When we want to talk about a series of lessons or lectures we attend, we say we take a course. The same term applies when we want to talk about a period of study at an academic institution which leads to an exam or qualification, as in postgraduate courses.

According to OALD, class can also be used to describe a series of lessons on a particular subject (as a synonym of course), for example we can say pottery class and mean a series of classes/lessons.

In a "class" you take lessons.

In a "course" you take many classes.