What have you tried so far?

We mush up a little canned puppy food with milk and put it on our finger.
Puppy sucks on finger and gets a bit of food. As the pup gets used to the sensation of food in its mouth your can try less milk so it's thicker, and eventually put the food on a saucer and just push small amounts towards the pups mouth.
They get the hang of it eventually and start eating from a plate.

Don't introduce any more than a teaspoon of food the first day or you will end up with either the runs or constipation.