USAGE OF AT

aT
used to say where something or someone is or where something happens
at the corner of the street
We transferred at Grand Central.
They arrived late at the airport.

used to say where someone works or studies
He's been at the bank longer than anyone else.
She's at Yale (= Yale University).

used to say when something happens
We left at 2 o'clock.
at the end of the week
We woke at dawn.

used to show the situation someone or something is in, what someone is doing, or what is happening
The country is now at war.
I felt like I was at a disadvantage.
I think Mr. Harris is at lunch.

in the direction of or toward someone or something
What are you looking at?
He pointed a gun at her.S
omebody threw stones at the protesters.