It is very easy to get confused between face contouring and bronzing and many people refer to them as the same thing. With contouring you are essentially accentuating the assets that you face has such as cheek bones and lips but with bronzing you are making certain appears appear more sun kissed. For example, with bronzing you would apply bronzer to the t-section of your face, making it look slightly tanned where the sun would normally catch you, but with contouring you would want to highlight these areas as this is where the light naturally hits your face. You would also contour the areas of your face with a darker colour that normally form a shadow to make a stronger definition between the two areas.
Any bronzing or contouring should be done gradually as over doing it can end up looking awful and give you quite a muddy complexion.