Dry dog food should be introduced to puppies at about three to four weeks old. At first try adding a small amount of warm water to mash down to a gruel. Avoid using cow's milk as this can cause diarrhoea. The food should be offered in a shallow bowl.
At first your puppy will only consume small amounts of the gruel. However, at around five weeks your puppie's teeth should be developed enough to more readily consume the gruel. At this point you should be able to move them onto dry kibble.
Weaning is usually complete at around 6 weeks of age, although it's not unusal for a puppy to continue to suckle occasional at 7 weeks.