My book 'Born On A Blue Day' is currently being edited for its US release in January and it's fascinating to compare the two forms of English - British and American.
A lot of it comes down simply to spelling, to 'z's instead of 's's as in 'realize' (where I would write 'realise') and absent 'u's ('color' and 'harbor' instead of 'colour' and 'harbour'). Words of foreign origin are also spelled differently: 'synesthesia' where in Britain it is 'synaesthesia'.
More interesting are the different words, some of which I didn't realise/realize were used in that way. For example the American for 'pram' is 'carriage' (an old-fashioned word to British ears), a 'conker' is a 'chestnut' and a 'plaster' is a 'bandage' (something a British hospital would only use for serious wounds, not just a scratch or bruise).
George Bernard Shaw was perhaps right when he observed that England and America were 'two countries separated by the same language'.