There is no single American English although some have labelled a certain type of American accent as "standard American English" (Some even go as far as to label it "Standard English" All Americans do not speak the same way of course but there are many common aspects of spoken English in the united states which can be recognized as being distinctly American as opposed to British. Rhetoric - r sound
Most Canadians and Americans pronounce an r sound after the vowel in words like barn, car, and farther. Most of the early English speaking settlers to America originated from Ireland and Scotland where the spoken English is of a rhetoric 'r' variety. So the way of pronouncing an 'r' sound after the vowel in words like 'bird' 'docter' etc., is far more common in the uSA than it is in the British Isles, although both countries have both types of speaker.
In modern times British people have more experience of American English than American's have of British English as The united States is more isolated both physically and culturally from the rest of the world. Characteristics of American English These so called "Americanisms" can appear in pronunciations, spelling, and grammatical constructions. There are a few words of genuine American origin, such as "Okay (OK), moose, opossum, squash, moccasin, tomahawk, totem and many old English words which these days are not so common in Britain but widely used in the States.

Generally Canadians have a similar accent to Americans and the rest of the English speaking world are closer to the British. Strangely the North West coast is closest to British English although furthest away geographically. It can be said that Canadian English is generally closer to British English and the English from the Southern States is the furthest from British English. One prominent difference between American English and Canadian English is the dypthong vowel sound in "How now brown cow"

In some cases there are differences between American English and British English in word stress. For example in these words: secretary, garage, Other words have fundamentally different sounds composing them. For example: schedule, zebra

American English spelling differs from British English spelling largely because of one man, American lexicographer Noah Webster. In addition to his well-known American Dictionary of the English Language (1828), Webster published The American Spelling Book (1783, with many subsequent editions), which became one of the most widely used schoolbooks in American history. Webster’s books sought to standardize spelling in the united States by promoting the use of an American language that intentionally differed from British English. The development of a specifically American variety of English mirrored the new country’s separate political development.

The grammar of educated speakers of English differs little among national varieties. In the speech of people with less access to education, grammatical variations in regional and social varieties of American English are very common as normal, systematic occurrences (not as errors). One major difference between British and American English is that the two attach different verb forms to nouns that are grammatically singular but plural in sense. In American English, the team is…, or the government is… (because they are viewed as single entities), but in British English, either plural or singular form could be used according to the feeling.

Most people around the world who learn English as a second language learn either American English or British English. The worldwide use of English began when Britain created a worldwide empire. Today, most people who learn English as a foreign language still learn British English. This happens because Britain has had a longstanding interest in teaching English and has publishers and institutions in place to promote it. American English is taught more and more, however, because of the worldwide success of American business and technology. This success also leads speakers of British English—even in England—to adopt many Americanisms. English has truly become a world language in science and business, and over time it will come to have more of an American English sound.