Oh—can't you stop making so much noise?
Oh, sir! You forgot your keys.
Oh, I see. You can't come until tomorrow.
Oh, oh, oh.
"You should watch where you're going!" "Oh?"
When a ghost surprises you in a haunted house, that's an example of when you say oh.
Calling a waiter to your table to bring you the check is an example of oh; "Oh, waiter."
When a student understands the math lesson they've been taught, they might say oh.
My telephone number is four-double-three-two-oh-nine.
Oh, when will it end?