"Organise" and "organize" both mean to arrange or structure systematically, but "organise" is British English while "organize" is American English.
(Fwiw, I spell "-ise". And "color". Thus "colorise". That's the vastly superior spelling that nowadays only I use (well, and some other holdouts like me), but used to be much more common in Australia. Some people just got the whole "America", "Britain" and "Australia" thing co...