Looping an animation?

I've got so many animation questions it's ridiculous, but hopefully someone here is partially qualified

So how do I loop an idle animation? If I export it as a looped animation then it won't ever let me change the animation from it to another one(for say, walking). I also want to loop the walking animation to make it less choppy instead of it firing over and over.

How do I just make the animations smooth like default animations? Are the default animations looped? What does priority do? Am I supposed to end looped animations to fire new ones?

local Humanoid = script.Parent.Humanoid

local animController = Instance.new('AnimationController')
animController.Parent = script.Parent

local Animations = {
    Walk = {id = 'rbxassetid://166955430'},
    Idle = {id = 'rbxassetid://166961426'},
}

local Animation = Instance.new("Animation")
function PlayAnim(Anim)
    Animation.AnimationId = Anim
    AnimTrack = Humanoid:LoadAnimation(Animation)
    AnimTrack:Play()
end

local Running
Humanoid.Running:connect(function(Speed)
    print(Speed)
    if Speed < 1 then
        Running = true
        PlayAnim(Animations.Idle.id)
    else
        Running = false
        PlayAnim(Animations.Walk.id)
    end
end)

while wait(30) do
    script.Parent.Humanoid:MoveTo(Vector3.new(math.random(-200,200),4,math.random(-200,200)),Game.Workspace.BasePlate)
end