Especially when you are a writer you will find “mistakes” in the English language when you read it. However these are not mistakes and even though it often sounds the same, the spelling and grammar differ in many instances.
Accent
When comparing accents between British and American you will find it difficult unless you are a pro. This is because in both UK and US they have their own differences too. However the trained ear knows when they speak to a New Yorker or to a Texan to use an example between two American English while even in the UK you get different British English between Glasgow, Manchester and London.
Spelling
Some simple examples regarding to spelling of the same English word include the following:
British English – American English
Colour – color
Behaviour – behavior
Theatre – theater
Metre – meter
Organise – organize
Travelled – traveled
Vocabulary
British English – American English
Flat – apartment
Biscuit – cookie
Football – soccer
Chemist’s – drugstore
Plaster – band aid
Postbox – mailbox
Jumper – sweater
Trainers – sneakers
Cinema – movies
Chips – fries
Crisps – chips
Holiday – vacation
Grammar
You will find various differences in prepositions relating to the two English versions too. In American English you might say that you going to the shops on the weekend while in British English you will be going to the shops at the weekend. The Americans also say Monday through Saturday while the British say Monday to Saturday. Americans will ask what you do on Christmas while the British as what you are doing at Christmas. Then you will also find the Americans saying I ate too little while the Brits will say I’ve eaten too little. The British will also say I have been to the bar while the Americans would say I went to the bar.