Differences are recognised mostly through the spelling of a number of words such as
color/colour or flavor/flavour.
English uses 'our' at the end of the word, American uses 'or'
Word ending in 'ize' in American English are used as 'ise' in Brtish English.
Some propositions differ and often different words are used for the same item.
If you set the language setting setting on a 'word' document to American or British English and work on it, the differences in spelling or grammar are highlighted,