used when you want to get someone's attention or continue what you are saying:
Oh, look, I think that's Harry over there.
Milk, cereal, juice - oh, and put lettuce on the list too.
used when you are giving an answer to a question:
'Have you met his wife?' ' Oh, yes, I know her quite well.'
'I hope Jenny won't be angry.' ' Oh, no, don't worry about that.'
oh, okay/all right
'Can you lend me ten pounds?' 'Oh, all right, but only until tomorrow.'
used to make a slight pause when you are speaking:
I met your friend in town, oh, what's her name?
used to show that you are very happy, angry, disappointed etc about something:
Oh, aren't those flowers gorgeous!
Oh, how awful!
Oh, no! I've left my keys in the car!
Oh, good, you're still here.
oh, God/oh, dear etc
Oh, God, I forgot all about it!
Oh, well, never mind.
used to show that you are surprised about something:
'Frances has left her husband, you know.' 'Oh, has she?'
Oh, I didn't know that.