‘’ On ’’ and ‘’ nous ’’ in French, what’s the difference?

You noticed that in French we have two pronouns that we use in a very similar way: « on » and « nous »

NOUS :

« Nous » comes from the Latin nōs. It replaces « je » + one or more other people. We translate it as « we » in english.

ON :

Before becoming a personal pronoun, « on » was a common name. « On » was first spelled « om », then « hom » and came from the Latin « homo » same as the word  »homme » (man). Originally, then,  »on » meant « man » in general. But with time it turned into a pronoun and lost this meaning.
Still, that’s the reason why we conjugate « on » in the singular even if today the meaning is plural!

Today, it can refer to:

• an indeterminate subject unknown to the speaker and is equivalent to « someone ». For example, when a person inside a room says (not knowing who it is) :

« On sonne à la porte. » 
« Someone is ringing at the door. »

• a whole group of people, in the sense of « people ». For example:

« En France, on célèbre la Fête Nationale le 14 juillet. »
« In France, we celebrate the National Day on July 14th. »

• a general truth value, for example in proverbs:

« On n’est jamais aussi bien servi que par soi-même »
 » We are never as well served as by ourselves. »

• in the familiar register, it is very often used for the first person of the plural (in the sense of « nous »).
For example, someone with a group might say:

« Nous mangeons au restaurant ce soir.« 
« We eat at the restaurant tonight. »

In daily French, « on » has already replaced the subject « nous ». According to L. R. Waugh, in his corpus of conversational metropolitan French, « on » is used in 99% of cases, and « nous » only in 1% of cases!

So, in conclusion, when you speak, it is better to use  »on » to sound more natural, except in a very formal situation; then you can use  »nous », such as when you make an official speech, but it is quite rare.

In writing it is used more often, especially in formal letters addressed to the administration.

Voilà, I hope you understand better why we have this strange situation in French!