In this use, fussed almost never stands alone. People say they are not fussed, meaning they do not mind what happens, what you choose, or how it is done. Tea or coffee? They are not fussed. Sit here or there? Not fussed. It is a calm, easy-going ‘either is fine’, not a happy cheer and not a sulk. Though actually the word looks like the past of fuss, ‘to worry and hover’, this sense points the other way: you are not making a fuss; you have no strong wish. It is informal British English, very common in speech. Americans more often say I don’t mind or I’m easy. You can be not fussed about a thing (‘I’m not fussed about the colour’). A nearby British stretch is can’t be fussed, which means ‘can’t be bothered’ — too tired or unwilling to make the effort — so listen for the not versus the can’t.