Visas are valid for the length of time stated on them, starting on the date of arrival in France.
There are very big differences between visas, about purpose and length of stay.
Which foreign nationals are exempt from this visa requirement? List
The main kinds of visa are:
What type of visa do I need to transit through an airport in France? more
Visas are never issued in France, so they must be applied for in your home or another country. Generally, you should apply for your visa 8-12 weeks before your planned date of arrival in France.
What type of Visa to apply for? more