Duck boots are constructed of a rubber
just rubber soles) and leather
uppers. They're usually mid-length boots, reaching a few inches above the ankle
but not providing the high level of waterproof
protection that knee-length rubber boots do.
They are, however, completely waterproof at least to the extent of the rubber portion, and the leather section is sufficiently water-resistant that a wearer's feet wouldn't get wet while splashing in the rain or crossing a shallow stream. Duck boots are not meant for extreme conditions, but they're comfortable, well-insulated and quite good for warding off moderate amounts of water, snow, or mud.
Duck boots look nothing like the feet, or any other body part, of an actual duck, nor are they made from any actual duck parts. They will not enable you to walk like a duck or talk like a duck. But they might just help you hunt ducks in boggy terrain without getting your feet soaked, and that's probably the origin of their name.