Use “on” when you think of a place as a surface or a line.

A surface is the outside or top part of something, like a table.

A floor can also be a surface: “Their apartment is on the fifth floor.”

Here, a floor is treated as a flat area that something can be on.

We also say “on” for a river or coast, and for some public transport.

Public transport means buses, trains, and other vehicles that people can use to travel.

Use “at” when you mean a point or a place for an activity, as in “I’m at the station” or “He’s at work.”

A point is a particular place seen as a location, rather than as an area or surface.

“At” is less specific; “in” tells us the person is inside the place.

Here, “specific” means giving more exact information about where someone is.