How does reducing sugar reduce any substance?
A reducing sugar is any sugar that is capable of acting as a reducing agent because it has a free aldehyde group or a free ketone group.
A reducing sugar is one that reduces another compound and is itself oxidized; that is, the carbonyl carbon of the sugar is oxidized to a carboxyl group.
Reducing sugars can be detected by their reaction with Benedict's Solution.
Generally, Benedict's test detects the presence of aldehydes, alpha-hydroxy-ketones, also by hemiacetal, including those that occur in certain ketoses.
The equation can be further explained bellow-