Incubators can be made simple or elaborate. You need to contain heat and humidity at a constant level. 99.5F to 100.5F heat and about 50% humidity.
The simplest incubator is made from a styrofoam cooler with a small square of fine wire fitted to the bottom about 1 inch off the floor of the cooler. A 100 watt light inside will provide the heat and a shallow dish of water provides the humidity.
Follow the link to see other types of homemade incubators.