Why is sometimes the conjugasion for "we" is nous nous? How do I know when is nous and when is nous nous?

Salut, Miche!

If you see "nous nous" it has to be a Reflexive Verb or used in a reflexive manor.

Nous Nous voyons = we see ourselves/or each other

Nous Nous lavons = se laver = we get washed/we wash ourselves.

It's always best to provide an example of "where" you saw the "nous nous" in case there is another explanation.

Mme

I saw nous nous in "se trouver". What comes to mind is vous vous appelez, so I thought that verbs that begins with "se" have this pattern.

The conjugation "nous nous" is not correct in standard French. The pronoun "nous" typically refers to the first-person plural subject pronoun, meaning "we" in English. However, there are instances where the pronoun "nous" is repeated for emphasis or clarification, which results in the incorrect and redundant expression "nous nous." This double usage of "nous" is considered a mistake or an incorrect repetition.

So, to answer your question, the correct conjugation for "we" is simply "nous," without repeating it. This is the default form used in most cases. For example, "Nous mangeons" means "We eat."

To avoid making the mistake of using "nous nous," always remember that using the pronoun "nous" once is sufficient to indicate the first-person plural subject pronoun. Only repeat it for emphasis or clarification when necessary.

If you come across the phrase "nous nous" in a text or conversation, it's likely an error, and you should treat it as such.