A proper noun is the name of a specific person, place, thing, or a title such as the heavy metal band 'Pain' or The Pain Management Center in Lansing MI.
They are born common nouns. Common nouns are words for any person, place, thing, or idea: person - man, teacher, mother, grocer, ballerina, neighbor place - country, capital, city, ocean, wildlife...
"Apple" is a noun. Generally it is a common noun, e.g the apple tasted good. It can, however, also be a proper noun when used as a name, e.g, Apple Inc.
You is neither a proper noun nor a common noun. You is a pronoun, specifically a personal pronoun. A pronoun is a word that replaces or substitutes for a noun or noun phrase. Personal pronouns...