For example: This is MY book. "Mine" is a shorter way to say "my book." Tom: May I have this book? Mona: No, I'm very sorry, but this is MY book. I need it. Tom: Please! Please! Let me have it! Mona: I told you that it was MINE. Now go away and stop bothering me!

"MY" is a modifier before a noun, e.g. "my apple/ laptop/ book" --> indicating that it belongs to me "MINE" is a possessive pronoun, so if you already clarified in an earlier part of the sentence what belongs to you or if it is clear by context, then you can replace that possession with "mine", e.g. "That is my apple. It is mine." Hope it helped, I am also learning English and find grammar both fascinating and intriguing ;)