Answer :
Carbon monoxide is a carbon atom bonded with an oxygen atom. Carbon dioxide is a carbon atom bonded with two oxygen atoms. That's it really, they have different properties but that is significantly more detailed and all a result of their molecular formula.
Carbon monoxide is 1 carbon and 1 oxygen, as in CO, or C₁O₁, and carbon dioxide is 1 carbon and 2 oxygen, as in CO₂