I usually hear it used sarcastically. It has many meanings: congratulations / good for you / great job / bravo / you win / you're right. Here is an example of when a person might use it: Girl 1: I got a B on the exam. What did you get? Girl 2: I got an A. I win! Girl 1: Well, bully for you!

It's a bit old fashioned, at least in the US. It means "congratulations" or "good for you." It is sometimes used sarcastically.

Your friend is right. It doesn't mean 'I agree with you' at all. It's a rather rude and dismissive comment meaning 'Well done' or 'Aren't you lucky?', always delivered in a sarcastic tone. It's also quite outdated. I doubt whether many young people would even have heard of it. I've no idea where you got this phrase from or who told you that it meant 'I agree', but I suggest you forget about it.

I think that means prefect ideal and totally agree with you.