I didn't apply to university.
I went through "classes préparatoires" to try the exam entry for "Grandes Ecoles".
You have one week of written exams, a good part of the people are eliminated, other goes for a second round of oral exams, and then the best marks can select their school first.
Some schools have an independant exam, some are grouped.
I succeeded the exams for ENAC (French Civil Aviation University, the one I selected), the ENSIETA (French "arms" school to learn how to build tanks, planes, ships...), and a common exam with 30 schools, but my marks were average, and I could have selected the most popular ones.