How do I make a portal?

I tried using this video to try to make a portal, but it’s a lot harder than I thought. I can’t get it right for some reason. He said to move it back through the wall How were the portals in Portal created? | Bitwise - YouTube at 2:42, but I think it just made it worse. At 4:08, he says to crop it down and scale it up, but I have no idea how to do that. My script so far

local guipcf = script.Parent.GUI.CFrame -- the surface gui's adornee
local camer = -- the red block
	cam2.CFrame = CFrame.lookAt(Ccam.CFrame.Position,guipcf.Position)
	local mag = (Ccam.CFrame.Position-script.Parent.GUI.Position).Magnitude
	cam2.CFrame = - cam2.CFrame.LookVector*mag) * CFrame.Angles(cam2.CFrame:ToEulerAnglesXYZ())
	--cam2.CFrame = cam2.CFrame - cam2.CFrame.LookVector * mag
	--cam2.CFrame = Ccam.CFrame
	--cam2.CFrame = - Ccam.CFrame.LookVector*mag)
	--cam2.CFrame = CFrame.lookAt(Ccam.CFrame.Position,script.Parent.GUI.CFrame.Position)
	--local cf = CFrame.lookAt(cam2.CFrame.Position,Ccam.CFrame.Position)
	--cam2.CFrame = cf * CFrame.Angles(cf.Rotation.X,cf.Rotation.Y+math.rad(180),cf.Rotation.Z)

the 3 things so it maybe doesn’t get removed

  1. What do you want to achieve? portal camera
  2. What is the issue? it just aint right
  3. What solutions have you tried so far? The whole video, and tried looking at the portal tech demo

You can see Egomoose’s portal script

Well does anyone know how to fix the camera? the egomoose portal thing is too complicated for me.