How do you use AnimationController?

I've read the tutorial, what I'm concerned about is how the "ID" of the animationcontroller is not connected to the "HumanoidRootPart", yet you can just play the animation and have it magically work?

Wait(3)
local animController = Instance.new("AnimationController")
local animTrack = animController:LoadAnimation(script.Idle)
animTrack:Play()

Well, if that's the correct way to do it then it doesn't work. I loaded it into animationcontroller, so why wouldn't it work?

You can't play with AnimationController. AnimationController don't have id Here's the code

Wait(3)
local anim = Instance.new("Animation")
local animTrack = anim:LoadAnimation(script.Idle)
animTrack:Play()