Depends what type of road you’re on, but as a general rule it’s as the stickers on the back indicate: 60, 80, 90
60 on secondary routes
80 on main roads where you have ‘priorité’ (indicated by the yellow diamond sign). Often 80 for trucks on two or three lane ring roads i.e Bordeaux rocade, Toulouse périphérique, etc
90 on autoroutes, unless ADR.
Plus 50kph within town/village limits (indicated by the red/white name boards) unless otherwise indicated - can be reduced to 30 for trucks in certain instances
That’s just a basic resumé, the older and/or wiser will obviously elaborate on these in greater detail.
~ Craig