Prepositions tell us where or when something is in relation to something else. When monsters are approaching, it’s good to have these special words to tell us where those monsters are. Are they behind us or in front of us? Will they be arriving in three seconds or at midnight?
Prepositions often tell us where one noun is in relation to another (e.g., The coffee is on the table beside you). But they can also indicate more abstract ideas, such as purpose or contrast (e.g., We went for a walk despite the rain).

I. Preposition in, on, at

A. Words to tell about preposition
a. In
We use ‘in’ to talk about position inside a larger place or space
There is a fish in the aquarium.
I prefer to sit in the front row.
b. at
We use ‘at’ to talk about:
1. A place considered as a point, not space.
There are students waiting at the bus stop.
There is a big tree at the corner of the street.
2. A specific place
Ghania was at her grandmother’s house.
Write your name at the bottom of the page.
3. An address
He arrived at 38, Kesatuan Street.

c. on
We use on to talk about the position at the top a surface or a place we think of as a line or flat.
There are some oranges on the table.
Don't sit on the grass.
B. The uses of in, at, and on for specific prepositions
1. In/at/on the corner
a. ‘In the corner’ shows the corner position inside a space . we say ‘in the corner of kitchen.’
 The refrigerator is in the corner of the kitchen.
b. ‘At/on the corner’ shows the corner position considered as a point in area.
We say ‘at the corner (or on the corner) of a street’.
 There is a big tree at/on the corner of the street.
2. in/at/on the front – in /at/on the back
a. ‘in the front/in the back’ shows the front/back position inside a space.
We say ‘in the front/in the back of a car.
I’m sitting in the back of the car and enjoying the view.
b. ‘at the front/at the back’ shows the front/back position considered as a point.
We say ‘at the front/at the back’ of a building/hall/cinema/group of people’, etc.
The garden is at the back of the building.
c. ‘on the front/on the back’ shows the front/back position on the exterior of a surface or flat object.
We say ‘on the front/on the back’ of an envelope/letter/piece of paper, etc.
Write your name on the back of this envelope.

II. Preposition Under, Above, In Front of

1. Under
We use ‘under’ to talk about a lower position and usually covered by another.
There are shoes under the chair
The pillow is under the blankets.
2. Below
We use ‘below’ to talk about a lower position than another with no direct contact.
The sofa is below the paintings.
The shoe shop is below the bookstore.
3. Above
We use ‘above’ to talk about a position higher than another.
There is a clock above the shelves..
The bookshelf is above the desk.
4. in front of
We use ‘in front of’ to talk  about a position further forward than something/somebody, but not very far away.
They sit in front of the TV
There is a coffee table in front of the chair.