Because the Geneva Airport is very close to the French border it has a French sector. The French sector is located near Ferney-Voltaire France just before its border crossing into Switzerland and is accessible via road - see video. When passing through the French sector you bypass Switzerland and Swiss immigration and customs.
When arriving on an international flight must go through Swiss passport control and customs before heading to the French Sector passageway on the upper level in departures. If you arrive on a flight from France you can go directly to the French Sector.
When flying into the Geneva airport you should only use the French sector if you have a reason. This is because the exit of the French sector, near Ferney-Voltaire, is not really centrally located and it is not east to find your way around unless you know the area and where you are going.
If you are traveling to any ski resorts in the Alps, then do not use the French sector. When going through customs exit into Switzerland and then go to France via Switzerland. You will have to cross the border into France but this is the quickest way. The chances of you being stopped at the border are very slim.
If you can't enter Switzerland but would still like to use the Geneva Airport to access the French Alps please see how to bypass Geneva.
The French sector is much smaller than the main airport and therefore has fewer services.
The French sector can be accessed from the main terminal. There is an entrance on the departures level near the British Airways check in desks. Look for a sign marked ‘destination France'. This will take you to the French Sector.