Confianza means trust. It also means familiarity between people.
De confianza, a person one can rely on, or a close and intimate one.
En confianza, in private, between people who trust each other.
Agarrar confianza, to grow at ease with someone over time.
Pásale, con confianza, “come in, make yourself at home,” said to a guest.
Tomarse confianzas, to take liberties, to act with more familiarity than the relationship allows.