You can buy a single ticket that includes travel on AS and French Bee. Such a ticket might come up when you search for an itinerary involving cities served by the two airlines. For example, if I look on Google Flights for ORY-SEA travel, French Bee itineraries connecting to Alaska (through SFO, LAX, or EWR) come up for booking through online travel agents.

If they weren't interline partners, you couldn't buy such a ticket. For reference, most of the major airlines are interline partners with most other airlines (with the notable exception of Southwest, which has few if any interline partners). It's the lowest level of partnership.