As soon as you take them out of the box, dip their bills in the water of their waterer in their brooder and make sure they swallow a drop do this one by one as you unpack them. When they are all unpacked make sure each one takes a drink on their own.  This makes sure they know where the water is and have at least a sip.  This is probably the single most important thing on day one.  If you can't get special duckling food, you can use unmedicated chick crumbles, but they will need additional niacin.  I put it in their water from capsules, many people add brewer's yeast (not baking yeast) to their food.  I also put probiotics and electrolytes in their water the entire time in the brooder.  (That is why I do the niacin in the water, I make 2 one gallon pitchers of "duck water cocktail" at a time and fill their waterer from them.  Then the food can just come from the bag.) It seems that a lot of problems I read about with ducklings are due to deficiencies, so I don't want to take any chances there.