The difference between American English and British English

These two are rather considered dialogues rather than separate langauges (like those of Chinese dialogues). While they're based on the same grammatic system, there are minor differences between the two.
Textually, it's usually spelling that changes.For example, the word 'colour' in British English is spelled. as 'color' in American English. Another word: 'centre' in B.E. is 'center' in A.E. In many occasions, endings also have changes. Like 'realise' in B.E., the -ise ending is reformed into -ize ending (realize).
In case of accent, there are generally two rules: the 'o' sound such as 'got' in the British accent is read as something like 'gaat' in American accent. Whereas full is pronounced 'fool' in British accent, it's read 'fuh-ll' in American accent. The 'a' sound in American accent resembles the pronunciation of 'e' more than that of 'ah'. Also, the ending -ther in British accnet does not emphasize the 'r' sound. For example, the word 'where' is usually just read 'weh,' whereas in American English, it is pronounced 'wehre.'
There may be other differences between the two Englishes. However, both dialogues can easily be understood the other since the differences are very minor.

in american english most words that end in "ise" are turned into "ize"
S's turn into Z's.
in british english words end in ise.