What's the difference between "lesson" and "class"?

I always have touble when using the "lesson" or "class".Are they synonyms or do they have something different?

PLEASE HELP ME~

class= lesson, but has more meanings:)

class means also for example "a group of people learnin' together" or also "category" 

Lesson and class would be synonym of each other, however if you would stress the differentiation between them, then here is my opinion:

Class would be more focus on who performs the activity e.g. group of students, group of pupils, group, and course group

Lesson would be more focus on what the group talking about; it could be lecture, session, topic, and tutorial.