Possessive pronoun, how to use them as "Stellvertreter" vs. "Begleiter"?

Answer 1

I believe this website explains it quite well. I summarized the gist of it but on the website you will find the declensions as well.

https://deutsch.lingolia.com/en/grammar/pronouns/possessive-pronouns

Dependent possessive pronouns (Begleiter) have to be used with the corresponding noun and come before it.

Example: Das ist mein Koffer. Hast du meinen Koffer gesehen?

Independent possessive pronouns (Stellvertreter) can stand alone and replace the aforementioned noun.

Example: Wem gehört der Koffer? – Das ist meiner.