Pronouns are used to refer to the two sides of a dialogue (I, my, mine, we, our, ours'\'; you, your, yours'') or to reduce repetition: `Julia called Julia's father, because Julia wanted to know whether Julia could use Julia's father's car'. is more compactly expressed as `Julia called her father, because she wanted to know whether she could use his car'.
These possessive pronouns are called determinative because they constitute determiner phrases.
These possessive pronouns are called independent, because they constitute full noun phrases and don't depend on a noun, i.e. while my must be followed by a noun such as glasses in my glasses, mine already subsumes such a noun.
For more information, see pronoun, noun, and possessionDeterminative possessive pronouns
There are seven of these in modern English: my, your, his, her, its, our, their
Older forms of English had one more: thy (`your') as in Thy kingdom come. It was used in familiar address, i.e., speech directed toward somone with whom one had a very close, perhaps family, relationship. Now this form only appears in poetic or religious use.Independent possessive pronouns
There are seven of these in modern English: mine, yours, his, hers, its, ours, theirs
Older forms of English had one more: thine (`yours') as in All glory and honor be Thine. Like "thy," this form currently appears only in poetic and religious contexts.