at

Expressing the target or direction of an action.

"She threw the ball at him."

Used to specify a price, speed, or rate.

"Sold at a discount."

Indicating a state, condition, or involvement in an activity.

"He is good at maths."

Indicating a specific location, position, or place.

"He is waiting at the bus stop."

Indicating a precise point or period in time.

"Let's meet at 7 o'clock."