Without this certificate, you will not be able to register
The CVEC is "intended to promote the reception and social, health, cultural and sports support of students and to reinforce the preventive and health education actions carried out for them" (article L. 841-5 of the Education Code).
By law, it is collected by the CROUS. The annual fee is €95. You may or may not be subject to it and, depending on your situation, you may be exempted from it.
Actions carried out with the Student and Campus Life Contribution
Paying the CVEC is a compulsory step for enrolling in higher education
To simplify your CVEC contribution, it is possible to do it online at https://cvec.etudiant.gouv.fr/. It is compulsory to present it when you register and it will also give you access to Crous scholarships and accommodation in residence. Note that Crous residences allow you to reduce your monthly expenses but you still have to pay for the daily expenses for your accommodation, see elec price the electricity rates in France for your accommodation.