American and British English differences: http://en.wikipedia.org/wiki/American_and_British_English_differences

There are differences in pronunciation, spelling, grammar, and vocabulary. If you are taking an English test, find out what it's testing: British English or American English. If you are learning English for your career, ask yourself where you think you'll be spending the most time - Europe (British English) or North America (American English)? As an American, I did have a few problems when I was in the U.K. Believe it or not, outside of London I had to ask people to repeat what they said because I wasn't used to their regional accents.

Sometimes UK do not use the word THE when talking about a place. They go to park when they go to the park. This is confusing when an american hears it because we have a meaning for going to park which is not the same as going to the park. Going to park means putting a car in a lot. So when I heard this I thought "but we are not in a car." There are many other examples such as going to hospital. Leaving the out makes it sound like an action rather than visiting a place to an American.

Virtually no difference besides the accent. I'm only aware of a few words the English use that we say differently. Cell phone: in the US we say: cell phone, or cell. In the UK they say mobile. Television. In the US: T.V.. In the UK I think they say telly. The slang is pretty different though. They seem to say "wicked" a lot in the UK to say something was cool, good or great. For example: That was a wicked party. In the US slang words for something being cool, good or great seem to change so often I don't even know what the current trendy word is.