Spanish speakers use tú and usted, which both mean “you,” to convey the formality of a relationship. Tú is less formal than usted.
You use tú when you’re talking to someone of the same age, the same rank, or the same educational level. When you’re talking to a close friend or a family member. You can also use it when you want to express a certain level of intimacy with someone. Most adults address children using tú.
Usted signifies a more respectful way of talking to someone, such as a new acquaintance, an older person, or someone you consider to be of higher rank.
At some point in a relationship between people who speak Spanish, a shift occurs from the formal usted to the more informal and intimate tú. At this point, they use the word tú when addressing each other. In Spanish, we call this tutearse, that is, “to talk tú.” On the other hand, if you don’t want to have a closer, more intimate relationship with someone, or if you want to keep the relationship more professional and less chummy, you should stick to calling that person usted.