The chief prepositions used to talk about place are: at, on and in.

At is used to talk about position at a point. At can also be used with a larger place when we think of it as a meeting place or a stage on a journey.

The plane does not stop at Bangkok.

I met her at the library.

At is also used with proper names used for buildings and organizations.

Compare:

She works at HSBC.

She works in a big bank.

At is also used to say where people study.

She is at Harvard Business School.

On

On is used to talk about position on a line.

Banaras is on the river Ganges.

On is also used to talk about position on a surface.

There is a spider on the wall.

She sat on the bench.

Put the books on the table.

I think we should hang this picture on that wall.

On can also be used to talk about things attached to something.

She was wearing a diamond necklace on her middle finger.

There are many apples on the tree.

In

We use in to talk about position inside large areas.

She was born in England.

He had to live in the desert for three years.

In is also used to talk about position inside three-dimensional space.

There is some water in the bottle.

She put the money in the box.