Confused usage of American English and British English

To learn a language and learn it well, one should use a good dictionary. For the learning of English Language, by the way, in Singapore, we are using British English and I have found Collins Cobuild English Dictionary a good one. Incidentally, I have always noticed the confused usage of American English and British English. Should it be centre or center, colour or color, practise or practice (as verb), advise or advice (as verb), metre or meter, favour or favor, organise or organize, synchronise or synchronize etc. Are you confused? Check it out in the dictionary yourself.