Cool is slang from a few decades ago that seems to have stuck around. Basically, "cool" can be used to say that you think something is really good, with the implication that you also like it, eg. "That's really cool." People will sometimes just say "cool" as a form of acknowledgement to something that has been said or to indicate they understand what has been said, sort of similar to the use of "okay." eg. Person 1: "Tomorrow we're going to see a film, okay?" ; Person 2: "Cool." In this example, Person 2 is essentially indicating "Yes, okay, I understand."

I think that the American culture is trying to destroy you Chinese culture. It aims at the most sensitive spots - children and youth. In Russian it's bad taste to say cool, we are a great nation and we find it laughable to copy stupid words, but we love some good american TV shows like the House M.D. or the Lost. Don't copy the stupid things like cool.

I think，the Chinese equivalent is 酷，很酷。'Cool' is a adjective, while 噢 is an interjection, the english equivalent of which is 'oh' or, in some cases, maybe 'wow'.