Yes, there are a few differences between the US and UK spellings, the most common being: 1) the -our ending in the UK and the -or ending in the US See examples given by fowlertm 2) the -ise verb ending in the UK and the -ize verb ending the US For example: realise versus realize, optimised versus optimized, etc. 3) the -ogue ending in the UK and the -og ending in the US For example: catalogue versus catalog, dialogue versus dialog, etc. 4) the -ce ending in the UK and the -se ending in the US For example: licence versus license, defence versus defense, etc. 5) the -re ending in the UK and the -er ending in the US For example: litre versus liter, metre versus meter, theatre versus theater, etc. 6) the use of -ll- in the UK and -l- un the US with verbs ending in 'l' For example: cancelled versus canceled, dialled versus dialed, etc. There are other differences, but these are the main ones, I think.

Yes, they are usually different in small ways but not big ways. If you learn American spelling British people can read it easily, and if you learn British spelling American people can read it easily. One example are the words "color", "honor", "valor", etc. In America they end in 'or', in Britain they end in "our". So they become "colour", "honour", "valour". There are probably other examples, but the spelling is very similar.