-This is the difference between my and mine

My and mine, while both possessive pronouns are used quite differently

My is placed right before an object.

Example: "This is my pencil." "Would you mind getting my book over there?"

Mine refers back to a previously known object.

"Look at that book! It's mine!" "She thought it was hers, but it was actually mine."

-This is the difference between at and in 

When talking about location, in is generally used for a larger area where there are numerous specific locations possible

I am in the United States.
I am in New York.
I am in the Chelsea neighborhood.
I am in my backyard.

The preposition at is generally used for a specific location or thing.

I am at the intersection of Hollywood and Vine [streets].
I am at the Empire State Building.
I am at my hotel.
I am at home.
I am at the old oak tree in my yard.

However, the above at usage is indifferent to whether you are indoors or outdoors. You could be on the street in front of your hotel or inside. You could be in your yard at home or in the bathroom at home.

If you want to convey that you are indoors at a specific location, you would use in

I am in the Empire State Building.
I am in my hotel.
I am in my home.

The above conventions reflect an American usage which may or may not be similar in other English speaking countries.

I hope this will help

What is the difference...

What is the difference between ?

mine ,my
and

at,in 

I am not a teacher but I can give you examples: 

This book is MINE.  

This pen is MINE.

My book is not yours.

My backpack is in the trunk.

I will go to my house

Which backpack is yours?  The one with the stripes is MINE.

A little slang lesson here: Where are you?= Where you at? (slang)

I am at the store.  It means you are at a place.

I am in the store.  This means you are inside, in a specific place/area/city. 

I am AT cairo= No, you cannot say this.  You have to say: I am IN Cairo.

Where are you?  

I am at school.  (but this answer can mean you are outside the school but IN the parking lot)

Where are you?  

I am in the car. (this means you are INSIDE the car)

I am at the car.  ( This means you are outside the car... or near the car.)

Where are you?

I am AT work.  

You cannot say " I am IN work."  You have to say I am INSIDE working.  or I am IN my workplace.  

What is the difference...

What is the difference between ?

mine ,my
and

at,in

1. Mine - a possessive pronoun. It takes the place of the subject noun.

" I own a car. Mine is red. What color is your car?"

2. Mine - a possessive adjective. It describes the ownership of the subject object in a sentence.

" The red car is mine. I own it."

3. A mine - (noun) - a mine is a hole in the ground to dig metals, coal, and other materials.

" He works in a mine. It is dangerous work."

4. A mine - (noun) - (a landmine) a military ground explosive that is hidden. It explodes when stepped on. A naval weapon dropped into harbors.

" The soldier stepped on a mine and was killed. "

" The boat hit a mine and sank. "

1. My - a possessive adjective. It describes the ownership of the subject object in a sentence.

" My car is red. It is mine. "