At present, most universities implement the credit system. In this case, if a course fails, it is necessary to retake the exam (a few schools can retake the exam), that is, to study again. You can study with your juniors, or you can go to advanced classes (usually some basic courses, such as advanced mathematics and English). In addition, most schools, even if they have passed a certain course, can still retake the exam in order to get higher scores.
Failing a course will have different consequences in different schools. Once some schools have a record of failing a certain course, they can't go on to graduate school or get some scholarships, and they don't have a chance to win some honorary titles. For almost all schools, if they fail to reach a certain number, they will be punished accordingly, such as warning to drop out of school, dropping out of school, extending the school year and so on.
The severity of failing the course depends entirely on the school. For those students who fail the course seriously, they can't get scholarships, can't keep graduate students, and there is nothing else.