A pronoun is a word that refers to either the people talking (“I” or “you”) or someone or something that is being talked about (like “she”, “it”, “them”, and “this”). Gender pronouns (he/she/they/ze etc.) specifically refer to the person you are referring to.
Pronouns are part of someone’s gender expression, and people can have multiple sets of pronouns for themselves (such as using both he/him/his and they/them/theirs). Pronouns are not “preferred” but instead are required for respectful communication. Not only transgender or nonbinary communities use pronouns, as it is something we all use and have since we were little.