Yes, correspondence is a form of self-study, supplemented by tutoring. Sign up at the correspondence school (it can be from other places), pay the tuition, and then the correspondence school will send you some books and reference materials regularly. At the end of the semester, the school will give you a test paper, usually an open-book exam. The paper will be written and sent back to the school within the specified time. After passing the marking, the results will be recorded. After passing all subjects and defense, you will get a diploma with corresponding academic qualifications. This is correspondence education. The "letter" here refers to letters, telephone calls, internet, video and television, that is to say, it does not mean face-to-face instruction. According to relevant laws and regulations, correspondence is equivalent to face-to-face academic certification. However, this form of education and diploma is not recognized in many parts of the country. In contrast, if you apply for full-time self-taught undergraduate courses, your recognition will be higher, or you will be promoted to junior college.