'What the hell', is one of the many ways of saying, 'so what' ! What difference does it make?
When I told my sister to comb her hair because it was all over she replied,'what the hell'! In other words she ment to say 'I really don't care'.
What the hell is also a very rude way of asking a question. You could say 'what the hell are you talking about'? You are asking him to explain what he is saying because what he has said it is so rude. It is best not to use these expressions because they are not polite. 'What difference does it make?' is not only correct English but it also makes you feel like a gentleman or lady