It can be used in various contexts:
* Time: "J'ai travaillé huit heures aujourd'hui." (I worked eight hours today.)
* Duration: "Le film dure huit heures." (The movie lasts eight hours.)
* Clock time: "Il est huit heures." (It is eight o'clock.)
The plural form "heures" is used for "hours" in general, while "heure" is used for "hour" in singular.