What's the difference between AMERICAN and BRITISH spelling?

This is not a quick question to answer, but once looking at it in terms of groups of words, it is not so hard.  There are two groups of words: Latin-derived and Greek-derived.  Keep in mind the abbreviations used here:

Am.E=American English 
Br.E=British English

Latin-derived Words

Humor or Humour?

Humor is American spelling while humour is British. Here are more examples...

Am.E=humor, neighbor, behavior, color, rumor, honor, flavor
Br.E=humour, neighbour, behaviour, colour, rumour, honour, flavour

Center or Centre?

Americans use the suffix "er" while the Brits use "re".

Am.E=center, theater, luster, somber, liter, meter, fiber

Br.E=centre, theatre, lustre, sombre, litre, metre, fibre

Greek-derived Words

Realize or Realise?

Americans use the "ize" suffix while their British counterparts use the "ise" ending. 

Am.E=realize, organize, recognize, apologize, modernize, colonize
Br.E=realise, organise, recognise, aplogise, modernise, colonise

Analyze or Analyse?

Americans use the "yze" suffix while their British use the "yse" suffix, a reverse of above.

Am.E=analyze, paralyze, catalyze

Br.E=analyse, paralyse, catalyse 

What is a homophone?

Homophones are words that have the same exact sound when spoken but are spelled differently in writing.  Here are a sample of homophones according to level to help you improve your writing:

 

Elementary

I=eye
hear=here
our=hour
sale=sail
their=they're
your=you're
you=´u´ (the letter)

 

Beginning

blue=blew
cent=sent
flour=flower
flu=flew
heel=he'll
new=knew
whose=who's

Intermediate

altar=alter
cellar=seller
cite=sight
genes=jeans
miner=minor
muscles=mussels
some=sum

 

Advanced

accept=except
aisle=I'll
bear=bare
principal=principle
site=sight
vain=vein
weather=whether