Personal pronouns represent specific people or things. We use them depending on:
number: singular ( I) or plural (we)
person: 1st person ( I), 2nd person (you) or 3rd person ( he)
gender: male (he), female (she) or neuter (it)
case: subject (we) or object ( us)
We use personal pronouns in place of the person or people that we are talking about. My name is Josef but when I am talking about myself I almost always use "I" or "me", not "Josef". When I am talking direct to you, I almost always use "you", not your name. When I am talking about another person, say John, I may start with "John" but then use "he" or "him". And so on.