How do PID controllers actually do anything?q

I'm both a brewer and a smoker, and someone suggested getting a PID controller. I have no idea how these work. I looked at PIDs on amazon, and I get that they register temperature, but so what? If the PID registers my smoker going above a temperature, it's not going to shovel coal around to adjust it right? What am I missing? Or for brewing, my gas stove doesn't have a plug to connect a PID. I admit I am a tech n00b, so if someone can just give me a basic answer. Thanks

Submitted April 02, 2016 at 01:22AM by blueberry_crepe http://ift.tt/1Rurb1x