American vs. British English
If you've been exposed to a lot of English you may have noticed differences in vocabulary and discrepancies in the spelling of some words. British colonization introduced the English language to the Americas in the late 16th and early 17th centuries. In the 400 years since the introduction of English to Americas, American English (AmE) has diverged from British English (BrE) in many ways. The differences between both are minor but significant enough for there to be a distinction between AmE and BrE.
Many of the differences in vocabulary, grammar, pronunciation, and idioms can probably be attributed to both versions of English evolving differently in their respective continents. In BrE, the influence of neighboring languages like French and Italian are more prominent than AmE. For example, the word for berinjela in AmE is eggplant, while the British use the French word, aubergine.
The differences in spelling between both versions of English have a more interesting story. English spelling was largely inconsistent for most of its history due to a lack of any kind of standard. That began to change in the 18th century. In 1746, Samuel Johnson, an English writer, was contracted to write a dictionary by London booksellers. The British standard of spelling began to emerge after publication of his dictionary, A Dictionary of the English Language in 1755. Across the pond, in the US, a standard for American spelling wouldn't emerge until 1828 when a man named Noah Webster published his dictionary American Dictionary of the English Language.
English is already a somewhat difficult language to learn because, phonetically, many words do not make sense. As a spelling reformer, Noah Webster preferred the spelling of words that more closely matched their pronunciation. While he did not invent the American spelling of many words, he was influential in making them popular and making them the standard in the US.
Examples of differences in American and British spelling:
theatre, litre, centre, fibre
theater, liter, center, fiber
offence, licence, defence, pretence,
offense, license, defense, pretense
recognise, apologise, organise
recognize, apologize, organize
behaviour, colour, humour, labour, neighbour, flavour
behavior, color, humor, labor, neighbor, flavor
Words ending in a vowel plus -l
travelling, traveller, fuelling
traveling, traveler, fueling
Many of the reforms made by Noah Webster do indeed make more sense phonetically, center more closely resembles the pronunciation than centre, and colour is pronounced the exact same as color. Despite these reforms, however, English is still a very difficult language to learn because of many words whose pronunciation does not match their spelling (e.g. laugh, through, psychology, knight).
Students often ask me how to know the correct pronunciation of a word and unfortunately there is often no clear rule. Often times the correct pronunciation cannot be deduced from the spelling, in such cases my advice is to ask an English teacher or use Google. If you're unsure of how to pronounce a word just ask Google, "how to pronounce (word)" and you'll have the answer for both American and British pronunciation!