An 'opinion' is the view somebody takes about a certain matter or subject. A 'fact' is something that can be shown to be true. Here are two examples:
One of them is an opinion and one is fact - do you know which is which? The first is a fact and the second is an opinion. Opinions are expressions of our beliefs. Facts, on the other hand, are expressions of what is true: even if we, personally, don't want to believe them.
See if you can get all ten questions correct in this 11-plus English quiz on fact and opinion.