What's the difference among:
- 自习 (zì xí)
- 自学 (zì xué)
They should be something like "to study by oneself", "to study on one’s own", but still, I don't get the difference.
学 more represent learning something new while 习 is more like review or revise, though you might learn something during review.
Confucious said: 学而时习之（学习 而且 时常 复习 它）, means you learn something new, but still need to review / revise sometimes.
The part you concentrate for 自 has no difference no matter "by oneself" or "on one’s own".
自习 emphasizes more on one's reviewing the knowledge points he has learned.
自学 emphasizes on one's teaching himself something where no teachers are available. In general, you don't have to go to school.
Also, 自习 or 自习课 could be a noun, referring to a session in school where the teacher is absent, or when present, the teacher doesn't teach any new material, and the students sit on their seat, do their homework, review the material, read words from textbooks and etc. I don't know if such a session exists in foreign countries. I remember I started taking this session from grade 6 in the primary school, and there are two sessions, in the morning and in the evening.
自习：practice by yourself. When you said 自习, you more like describing the action, rather than the content. Also you still have teacher to teach you, but you just practice by yourself when no teacher around.(but you still have a teacher)
Or you can think in this way: When you study in school, there are several study section. teacher teach you, practice when teacher around, practice when teacher not around. 自习 is the section to practice by yourself alone when teacher not around.
自习 describe an action.
自学：teach yourself without teacher. if you watch online video course or tutorial, it still count 自学. kind of that you should manage your study progress by yourself, and there is no teacher who can give you any feedback. When you 自学 something, there is no 自习 section because you study by yourself all the time and no need to divide into "practice by yourself" section.
自学 describe a progress and an ability.