The French are the people who live in France. What exactly one means by "France" can vary quite a bit depending on what year it is and who's talking.
The earliest extant French text is The Oath of Strasbourg, from 842 CE. The dialects of Old French are called collectively langue d'oil. Middle French developed around the end of the 13th century, and saw the end of the declension system.
French is now a widely-used language in Western Europe and is one of the five official languages of the European Union.