English pronunciation is not that easy for foreign students, many languages out there are pronunciated as they are wroten, but English is not, even an English Native speaker needs to ask about the pronunction of a new word. But it's OK, the secret is not worry about it. Whether you don't know how to pronunciate a word, ask someone who knows.
And yes, they are different, but not that different, I'd say, as a student, that "men" pronunciated by Britons is pretty close to "man" pronunciated by Americans. So, what can we do about it?
Well, I guess the best option is listen carefully all of them, different people all over the world, many movies, documentaries, something you like, you know... and accept them as they are, don't find them difficult, just have fun, it makes the learning process faster and easier!
Hope this helps!