Oh, it's been a long day, hasn't it? Oh, do you want a biscuit?

Questions are sentences which ask something. They end with a question mark. That's the funny squiggle with a dot over there. We use one of these instead of a full stop.

Often questions begin with a question word, like who, when or how.

Did you eat all the biscuits? Then who did? Oh! What about him? Oh, why does this always happen? I really fancied a biscuit too.