Look at these sentences:
N'importe qui peut entrer chez toiAnyone can get into your house
Elle fait confiance à n'importe quiShe trusts anyone
Juliette et Marie parlent à n'importe quiJuliette and Marie talk to anyone
Note that "n'importe qui" literally means "no matter who", and is used in French to say "anyone".
You use it ONLY in affirmative sentences to emphasise that the identity of the person referred to doesn't matter (ANY one).
You would use quelqu'un to express 'anyone' in a question.
Il y a quelqu'un ici ?Is there anyone here?
(See also Quelqu'un, Quelqu'un d'autre = Someone, Someone else (indefinite pronouns))
You would use personne in a negative sentence.
Non, il n'y a personne.No, there isn't anyone.
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