The controller typically has a number of relay terminals, one for heating and occasionally one for cooling, each with NC and NO contacts. The NO terminals for the heating output normally go in series with the heater; however, it is possible that the controller cannot handle the load of your heater. If this is the case you will need a larger relay or a solid-state relay with sufficient current rating for your heating element. The solid state relay may require a voltage source as well; try to find one with simple closure contacts for the control element.
There is another set of contacts for a thermistor, thermocouple, or current/voltage feedback. You would connect these to a sensor that is located as close as possible to the food. For a sous vide machine, this might be a probe that extends into the middle of the tank. Feel free to add more details if I can help more.
Interestingly, a good rice cooker would not use a PID controller, at least not exclusively, because you need to sense the temperature under a constant power input to determine when the rice has finished cooking, then switch to a constant-temperature mode to keep the rice warm without burning or drying it.