The word ‘school’ probably comes from the collective noun ‘School of thought’ indicating similar ideas. A school is a place where students come to learn.
In formal structure of education, the students are assigned to classes, and they progress according to tests and exams that are conducted to determine passage into the next phase.
The school employs people that are qualified to impart knowledge on the students and also guide them in all they do. These people are called teachers.
Of course just as each school varies, so does the structure. Some rural schools may have only a small building for classrooms and a large open ground. Schools at the other end of the spectrum may have sophisticated computer laboratory and a music room etc.