When we describe a position or a location, we often use the prepositions on, in, at. Here are a few common rules on how to choose a suitable preposition. Of course, there are exceptions and set phrases "preposition + noun".
on = on the surface
On is used to talk about horizontal or vertical surfaces. If you can think of something as a surface, you say "on". This surface might be smooth and even, like a shelf, a wall, or it might be uneven, like skin, fabric.
The plate is on the table. horizontal surface
The cushion is on the sofa. horizontal surface
The picture is on the wall. vertical surface
There's water on the floor. horizontal surface
You've got a nice print on your T-shirt. uneven surface
He's got a trace of lipstick on his cheek. uneven surface
Open the book on page fifty-eight. horizontal surface
The best price offers are on the main page of the website. on a webpage = on a page
on the left, on the right
on the list, on a menu, on a map
on the way
on a bus / on a train / on a plane / on a ship / on a bike / on a horse
on TV, on the radio
in = inside
We use the preposition "in" meaning "inside" or "within the borders". If you can think of something inside of a three-dimensional object like a box, a room, the air, the water, you say "in".
The pencils are in the drawer.
People are swimming in the pool / in the river / in the sea.
Mary's not in the kitchen, she's in the garden.
He lives in Berlin in Germany. He lives in the city centre.
Look! There's a huge dog in that car.
in a picture, in a photo
in the sky
in a car / in a taxi
in a line, in a row, in a queue
in hospital, in prison, in jail
in a letter, in a book, in a magazine
at = at a place, at an event
We use "at" in three main cases.
1) at = near the vertical plane of the object
Someone is standing at the door / at the window.
She's sitting at the table / at the piano.
2) at = at a place, a point (a location) on the map
Turn left at the junction / at the traffic lights.
People are waiting for the bus at the bus stop.
Let's meet at the airport.
We had lunch at Paulino's yesterday.
Keep in mind that when we speak about buildings, we choose between "at" and "in" depending on what we want to stress. If location is important, we use "at". If we want to say that something is inside of the building, we use "in".
We had dinner at the restaurant yesterday. (place)
It was very dark and stuffy in the restaurant. (inside)
He met us at the airport. (place)
I always enjoy myself when I'm in the airport. (inside)
3) at = at an event
There were a lot of people at the party / at the wedding.
We met at the conference.
We'll discuss these issues at the next meeting.
at the top / at the bottom (of a page)
at the front / at the back
at home / at work / at school / at university / at college