Craft or place a Campfire, Standing Torch, Air Conditioner, Dimetrodon, or Egg Incubator
Put the fertilized egg on the ground near the heat source or inside the Egg Incubator
Adjust the temperature until the egg shows it is in the correct range
Keep the egg at the proper temperature until the incubation bar completes
Pick up the hatched baby creature when it appears
Feed the baby the correct food immediately
Keep feeding the baby until it reaches juvenile stage
Use multiple heat sources or air conditioners if needed to maintain stable temperature