on
used for saying where something is
On is usually a preposition. You use on to say where someone or something is by mentioning the object or surface that is under them.
When I came back, she was sitting on the stairs.
There was a photograph of a beautiful girl on Deepak's desk.
On is used in some other ways to say where someone or something is. For example, you use it to mention an area of land where someone works or lives, such as a farm, building site, or housing estate.
He briefly worked on a building site in Seoul.
You also use on to mention an island where something exists or happens.
She lives on a Caribbean island.
used for saying where something goes
You can use on to say where someone or something falls or is put.
He fell on the floor.
I put a hand on his shoulder.
Onto is used in a similar way.
➜ See onto
You use on after get to say that someone enters a bus, train, or ship.
George got on the bus with us.
➜ For more information, see go into - get into - get on
used for talking about time
You say that something happens on a particular day or date.
She came to see the play on the following Friday.
Caro was born on April 10th.
You can sometimes use on to say that one thing happens immediately after another. For example, if something happens on someone's arrival, it happens immediately after they arrive.
‘It’s so unfair,' Clarissa said on her return.
used as an adverb
On is sometimes an adverb, usually showing that something continues to happen or be done.
She walked on, silently thinking.
I flew on to California.