Difference between American English (AmE) and British English (BrE)...
For all the examples I will say AmE first and then BrE.
Sometimes it is just the spelling (color / colour), (realize / realise), which you can learn the -or/-our and -ize/-ise difference
Sometimes it is a different word, but similar. It is pronounced and spelt differently. For example (mom / mum), (airplane / aeroplane).
In BrE for some verbs, instead or adding -ed, we add -t (although some people still add -ed): (spelled / spelt), (burned / burnt).
Some words are completely different: (candy / sweets), (cookie / biscuit), (sidewalk / pavement), (sneakers / trainers)
Words can be used differently, like AmE usually use "What's up?" to mean "How are you?", but BrE can use it to mean "What is wrong?".
There are some words like this: in AmE (practice = noun or verb), in BrE (practice = noun, practise = verb)
And you also have the same word pronounced differently, like with 'leisure', 'data', etc.
Like with 'water': AmE: wot-er, BrE: waw-ter.
For example, AmE say: eraser, BrE say: rubber. But in US 'rubber' = condom. So we will ask for a rubber at school, but in the US, they won't.