Some of the accents are very different, and a few words are spelled differently, and some slang is different. But ALL people from English speaking countries understand each other.So it is NOT important which "version" you learn, because they are NOT different dialects.

As everyone has said, it is the same apart from a few words. The US have dropped the 'u' in certain words such as the British 'honour' is 'honor'. Favourite is favorite. Then the s to a z in words like the British 'organise' is 'organize'. 'Recognise' to 'recognize'. Then trousers in British English is Pants in the US. Crisps in the uk is chips in the US. Chips in the uk is fries in the US. I hope this helps.

I agree totally with what Merlyn says. English is not like Arabic, which has such wide variations from one country to another that you have to make a choice which type to learn. Compared with the differences between the variants of Arabic, the differences between British and American English are so small as to be insignificant. There is only ONE English language, and it really doesn't matter whether you learn from a British teacher or American teacher - it's still the same language.

Accents can be different depending on the region of the US or UK, but the English itself really only differs in vocabulary. Certain things may have different names used in different places, even among those who live in those regions. The way in which English is spoken does not differ, however. Grammar and the like are all the same.

Part 2: -American accents don't distinguish between long and short /æ/ sounds ie. they pronounce 'bad' and 'cat' with the same vowel. -When 't' is at the end of a word, it's unaspirated in Australia (this is sometimes misheard as a glottal stop).'T' really is pronounced as a glottal stop at the ends of words in some English accents (I know someone from Oxford who does this... I don't know how widespread this is, but I think it's less common than pronouncing 't' as a glottal stop when it's between two vowels). -In Cockney accents, 'th' is pronounced as 'v' when it's voiced and 'f' when it's unvoiced. In some African American Vernacular accents, 'th' is pronounced as 'd'. -There are a LOT of accental differences when it comes to diphongs. I think this is the first thing you pick up on when you hear someone with a different accent. -There has been a tendency for /ɑː/ sound to change into /æ/ sounds. This is much more complete in American English, where just about every /ɑː/ sound has changed to an /æ/. In the UK and Australia, we say /ɑː/ in a lot of words where Americans say /æ/. The older someone is, the more likely they are to use /ɑː/. -There are some minor spelling differences between the US and the UK. All the Commonwealth countries and Ireland generally use the British spellings. I believe both the American and British spellings are used in Canada. There are of course other differences, mainly with vowels, but I can't really describe them with words. If I missed something or said something wrong, anyone's free to let me know.