Spanish has two you’s, just like in English where we have the
“you” =  you formal
and
“thou” =  you informal.

In English the “thou” form has become obsolete in daily life. However, in Spanish, both formal and personal forms are used. It is important to use them appropriately.

You usually won’t offend people if you use the wrong “you.” Spanish-speakers are very forgiving and usually appreciate the fact that you are trying to speak their language. If you don’t know a person, it is usually better to use the “you formal”  to show respect.

Women should use caution not to use the personal you (tú), with a man until she develops confidence in him. A man may misinterpret the use of the personal you as an invitation to intimacy. If a man is using the personal you (tú) with a woman inappropriately, she can simply say, Usted, por favor, and he will get the idea.

You probably won’t be on first-name basis with most people, so the formal you will be more appropriate most of the time.

OK, HERE IS A BASIC LIST OF RULES;

YOU formal (Usted) vs. You personal (tú)
The formal you (USTED) is used with:
1.    people whom you don’t know or whom you don’t call by their first name.
2.    people who are in authority over you, or to whom you wish to show respect.
3.    people who are older than you.
4.    people with whom you have no level of intimacy or confidence.
The Personal You (TÚ) is used with:
1.    people with whom you are on a first-name basis.
2.    people with whom you are on equal terms.
3.    people who are younger than you.
4.    people with whom you have a level of intimacy or confidence.