I'm learning English in advanced level and I have difficulties figuring out how to distinguish American from British .
I suppose this would be a huge problem for anyone whose learning techniques repeatedly changed from one accent to another!
There is an Italki article on the issue, written by an American teacher. https://www.italki.com/article/588/british-or-american-english#.VlYuX_nhCc0
I agree with the article.
The differences are very obvious to native English speakers, but we start from the common perspective that we speak the same language. From the perspective of a non-native speaker, the differences are very small, and are generally not even mentioned in course books as an issue until at least upper intermediate level.
In my view, it is inaccurate and unhelpful for EFL teachers to state that there are significant differences between US and UK English.
There are many, many differences, particularly in idiom and word choice, but also in orthography and punctuation, and even grammar. A lot of Googling will help you with the principal differences. Two examples that spring immediately to my mind:
#1 Adjectives stand in place of adverbs in much of American English
How are you? I am well. (Br) I am good. (Am)
Drive safe! (Am) vs. Drive safely! (Br)
#2 some (amongst** very, very many) word differences.
He is mad (Am) == he is angry
He is mad (Br) == he is crazy
He is pissed (Am) == he is mad (Am) == he is angry
He is pissed (Br) == he is drunk
What's up? (Am) == How are you doing?
What's up (Br) == What's wrong (with you)? As in are you OK? An expression of concern.
'Whilst' is pretty common in BrE writing (maybe more common than 'while'). In American English this is considered pretentious.
** amongst is perfectly acceptable BrE. In AmE it looks odd in writing, and sounds peculiar in speech.
Cheers is BrE can also mean thank you. In AmE it always means "cheers!" (a toast).
For the most part a Brit will understand an American, and an American is more likely to be confused by excessive Britishisms.
There are certainly many differences besides accent.
I agree with the poster above but I would say that "Drive safe" and "I am good" are not considered proper English in the United States in certain circles. I would never use "Drive safe" personally but I am not offended when others do. I think that it is okay if you use it colloquially but you know that it is not correct. "I am good" is very commonplace. In fact, some people might consider it pretentious to say "I am well" but do not use "I am good" in professional situations with educated American English speakers. No one will say anything because English is your second language but they will notice the error. I have caught myself saying "Good" when people how I am. It feels strange to hear myself say it but it makes me fit in better in casual situations.
Some other differences that come to mind:
B "Different to"
A "Different from"
B "What are you called?"
A "What is your name?"
B "Have you got?"
A "Do you have?"
Both of these are used but "do you have" is much more common in the US.
If you are in North, Central or South America or the Caribbean, I recommend using American English grammar and vocabulary. If you are anywhere else in the world, I recommend using British English. The accent is completely irrelevant until you are at native speaking level and even then it only matters in selected situations.
Also remember that within each country there are regional variations as well as variations based on age and situation.
Don't stress out about it.