On arrival in Rennes, you need to:
1. Confirm your registration at your host institution.
2. Undertake the relevant administrative procedures.
You are granted a "student" long stay visa equivalent to a residence permit (VLS-TS).
Upon arrival in France and within the first 3 months of your arrival in France you must validate this visa to the OFII portal in order for this visa to be considered as a residence permit.
Since February 2019 the OFII sticker is no longer affixed inside the passport but you must validate the visa online on :
After entered the number of your visa, provided the documents required and paid the tax of 50€ (by electronic fiscal stamp), you must confirm the registration of your visa to receive by email a validation certificate in PDF format.
This certificate must be saved, printed and kept inside the passeport during your stay in France and within the validity of your visa.
Payment of the electronic tax (electronic fiscal stamp) can be purchase online.
Within two months before your visa validated by the OFII expires, it will be possible to extend your stay without the need to apply for a new visa.
See procedure on the link « how to renew your long-stay visa/residence permit »