What do Japanese people do after finishing high school?
It depends on what type of high school you go. If your high school is for studying agriculture, fishing, business, nursing care, computer or technology for example, it is most likely to get a job after high school.
Many people go to university, if their finish a non-specialised high school（ふつうこうこう・普通高校）.
If you fail all the university entrance exams, you may like to go to a special school which is called ‘Yobiko（よびこう・予備校）’ after finishing high school. You study as hard as you can at the special school, so that you could enter a university in the following year.
Some of them go to せんもんがっこう（専門学校） where they can learn specific skills to become hairdresser, nurse, painter, farmer, musician etc. Generally speaking, it is not as hard as to enrol 専門学校, comparing with getting into a university.