How do we make Inverse Kinematics?

I never asked for the damn code mods so don't even try closing this. Just need some help with IK kinematics (aka dynamic movement) the problem is I don't know how the hell to make it and I get errors in the process of the code.

Code:

wait(1)
User = game.Players.LocalPlayer
Humanoid = User.Character.Humanoid
Torso = User.Character.LowerTorso
L_Hip = Torso["Left Hip"]
R_Hip = Torso["Right Hip"]

local step = game:GetService('RunService').RenderStepped;

function ArcTan(x, y)
	r = math.atan(y / x)
if x < 0 then
	r = r + math.pi
end
return r
end

vel = Vector3.new()
while true do
	step:wait()
	local velVector = Vector3.new(Torso.Velocity.X,0,Torso.Velocity.Z);
	if velVector.magnitude > 0 then
		m = (vel - Torso.Velocity).magnitude / Humanoid.WalkSpeed
		vel = (Torso.Velocity * m + vel * 2) / (m + 2)
		v = Torso.CFrame:pointToObjectSpace(vel + Torso.Position)
		L_a = ArcTan(v.x, -v.z)
		R_a = 3.1416 - ArcTan(v.x, v.z)
		L_Hip.C1 = CFrame.new(0, 1, 0)*CFrame.Angles(0, L_a+math.pi, 0)
		R_Hip.C1 = CFrame.new(0, 1, 0)*CFrame.Angles(0, R_a+math.pi, 0)
		L_Hip.C0 = CFrame.new(-0.5, -1, 0)*CFrame.Angles(0, L_a-math.pi, 0)
		R_Hip.C0 = CFrame.new(0.5, -1, 0)*CFrame.Angles(0, R_a-math.pi, 0)
		L_Hip.MaxVelocity = Torso.Velocity.magnitude / 100
		R_Hip.MaxVelocity = Torso.Velocity.magnitude / 100
	else
		L_Hip.C1 = CFrame.new(0, 1, 0)*CFrame.Angles(0, -1.57, 0)
		R_Hip.C1 = CFrame.new(0, 1, 0)*CFrame.Angles(0, 1.57, 0)
		L_Hip.C0 = CFrame.new(-0.5, -1, 0)*CFrame.Angles(0, -1.57, 0)
		R_Hip.C0 = CFrame.new(0.5, -1, 0)*CFrame.Angles(0, 1.57, 0)
	end
end

Quick Lil' Update, I think the motor6d's are just wrong and I think I may have named the whole thing wrong, sorry!