Newborn puppies, like all mammals, thrive on mother's milk. At three weeks of age, the weaning process beings as puppies try their paws at lapping water and diluted, mushy food. This is a fine time to introduce them to alternative sources of nourishment.
Newborn Pups' Nutritional Needs
From birth until about 3 weeks of age, a puppy's sole source of sustenance is mom's milk. During this time a puppy does not need supplemental food or water. Newborn pups nurse 12 times or more a day during their first week of life. At 10 days, their eyes and ears open and they become more mobile. Their stomach capacity increases, and they begin to nurse less frequently. At 2 weeks of age they nurse about six times a day.
At around three weeks of age, puppies begin to wean. They start eating and drinking and gradually give up nursing. Weaning is a process that takes two to three weeks to complete. Puppies' milk teeth begin to grow in at about 3 weeks of age, making nursing uncomfortable for mom. She begins to limit the amount of time the puppies can nurse. This motivates the puppies to start looking for sustenance elsewhere. Their motor skills have developed enough that they are ready to begin lapping water and diluted food.
When they're about 3 weeks of age you can introduce puppies to water by providing a shallow water dish outside the whelping box or sleeping area. Puppies at this age are beginning to explore their environments and will be able to find the dish. They will invariably make a mess. Good thing you didn't place it in their bedding. Expect the dish to get pretty dirty. It will require washing and refilling several times a day.
Introduce your puppies to food by making a mush for them to lap up. Place canned or dry puppy food in a blender or food processor with enough water to make a semi-solid gruel with the consistency of oatmeal. Puppies will end up wearing more of the gruel than eating it during their initial investigation into the world of food. This is a normal part of learning how to eat. When they're done "eating," mom will clean them off.