Usage of the Impersonal Pronoun On
The pronoun on is used in several situations:
Rule 1: to describe general facts.
French
Rule 2: to describe a situation in which the subject of the sentence is not known or deliberately not identified. We could use "someone" here.
French
Rule 3: in spoken French, it’s often used instead of "we."
French
Watch Out!
While the pronoun on is impersonal, it does replace the person or action made by the person. It can't be used instead of "it."