What does this joke mean?

It means that burning high school textbooks and review materials after the college entrance examination is just an outlet. After all, it is very hard and depressing during the preparation for the college entrance examination.

After the college entrance examination, some candidates choose to express their depressed mood by burning books. In fact, it is not necessary and should not be. After all, the days of senior three are unforgettable. These accompanying books are all records of candidates' struggle. Why not stay?

After the college entrance examination, you can choose many ways to adjust yourself, such as traveling, climbing mountains and watching movies. And you can catch up on your nap, look at the blue sky, get close to nature and look forward to the coming college life.