"my" is a possessive ADJECTIVE and must be followed by a noun ("book" in your example) "mine" is a PRONOUN and takes the place of a noun

I found a really interesting article which might be helpful for you. http://www.differencebetween.net/language/difference-between-my-and-mine/

Well... look at it this way: mine and yours my and your so basically it's the +s ver of my *My is used to mostly refer to humans, while mine is used for things. you wouldn't say yours book right?

my = my friend , my book . you mention ( my + the stuff ) . but mine = ex ( are this stuff yours ? , yes its mine ) just mention mine and there is no + the stuff . thats the most simple way to explain this diffrence .

me? i am sara.mine ?this book is mine