Usually pronounced as follows:
Aww, heeell yeah-us!
It is a strong affirmative, often shouted at sporting events, including college football and Nascar.
Less frequently, but still popular usage:
out of respect, while listening to good blues (said in hushed tones) as in- "oh, hell yes."
Last, but not least, sometimes used as a way of communicating pleasure, when with that special someone.
Oh, hell yes.