INFORMAL
Refers to people with whom you are familiar, same age group or people who are younger than you (children, etc.)
You (Subject Pronoun) – tú
Your (Possessive) – tu
Yourself (Reflexive Objective Pronoun) – te
Regular verbs would end with an “s” (-as, -es. -es)
FORMAL
Refers to people with whom you are unfamiliar, people older than you and people who are in authority over you.
You (Subject Pronoun) – usted
Your (Possessive) – su
Yourself (Reflexive Objective Pronoun) – se
Regular verbs would not end with an “s” (-a, -e. -e)