At, in and to

We use at and in to talk about position. To is used to talk about direction or movement.

I met him at the library. (Position)
He went to the library by bus. (Movement)
My parents live in Germany. (Position)
I went to Germany last month to visit them. (Movement/ Direction)

At is used after some verbs such as look, smile, laugh, frown, point etc., to indicate the target of a perception.

The children laughed at the beggar.
Stop throwing stones at the cat.
She stared at him.

He smiled at her.

At, on and in

We use at to talk about position at a point.

He met his wife at the club.
It is very hot at the center of the earth.

At is sometimes used with a larger place.
The train stopped for an hour at Frankfurt.

At is commonly used before the names of buildings or organizations.

She works at the State Bank of India.

At is also used to say where people study.

He is at the Harvard Business School.

At is also used before the names of certain group activities:

At a party
At a meeting
At a match
At a lecture
At a concert

We use on to talk about position on a river or a road.

London is on the river Thames.

On is also used for position on a surface.

The cat is on the table.
He sat on the bench.

In is used for position inside large areas.

She grew up in Africa.
The camel lives in the desert.

In is also used for position inside three-dimensional space.

We went for a walk in the woods.

We use on and off to talk about travel using public means of transport such as buses, trains and planes.

We are booked on flight 535.
As there was no room on the bus we got off it.

We use in and out of to talk about travel using private cars, planes and boats.