When a puppy is starting to wean off it's mothers milk and starts eating solid food you should really start the puppy off on eating wet food.
The wet food is much easier for new puppies to begin eating because they may not have all their teeth in which helps them chew the dry food better.
I've always started puppies off on wet canned food at 4 weeks and then after 6 weeks I switched the puppy over to dry food when they had more of there teeth in.
The puppy will naturally start eating the wet dog food once you put it out and there mother weans them off her milk supply.
Just like when you're feeding human babies you feed them really soft baby food as they get there teeth in and then you switch over to more solid foods for your baby when they get there teeth in more.
You should do the same with puppies as you can start them off with the wet puppy food and then switch them over to dry puppy food after 6 to 7 weeks.