Obtain a fertilized egg from two tamed creatures of the same species
Place the egg on the ground
Create the correct temperature for the species
Use campfires, standing torches, air conditioners, incubators, or other heat/cooling sources as needed
Keep the egg within the required temperature range until incubation completes
Wait for the egg to hatch
Pick up the baby creature immediately after hatching
Feed and care for the baby until it can eat from a trough or survive on its own