What else do I have to put in this script to make it work?

local isOpen = true

function open()
	isOpen = true
	script.Parent.D3.Transparency = 0
	script.Parent.D3.CanCollide = true 
	script.Parent.D4.Transparency = 0
	script.Parent.D4.CanCollide = true 
	script.Parent.D1.Transparency = 1  
	script.Parent.D1.CanCollide = true 
	script.Parent.D2.Transparency = 1  
	script.Parent.D2.CanCollide = true
end

function closed()
	isOpen = false
	script.Parent.D3.Transparency = 1
	script.Parent.D3.CanCollide = true 
	script.Parent.D4.Transparency = 1
	script.Parent.D4.CanCollide = true 
	script.Parent.D1.Transparency = 0  
	script.Parent.D1.CanCollide = true 
	script.Parent.D2.Transparency = 0  
	script.Parent.D2.CanCollide = true
end

function onClicked()
	
	if isOpen == true then closed() else open() end

end

I want CanCollide on at all times
D1,D2,D3 and D4 = Door 1, Door 2, Door 3 and Door 4.

Everything says true, which means Cancollide is on at all times. (put false to deactivate) I don't know the problem here...

Have you added a button to open these doors? Get a part, add clickdetector, put on the very top of script saying "function onclicked()" Make sure after the "end" of the second door set, it must have a mouseclick thing. Check through free models for that.

There are ceveral things wrong here.

1: your script you could use a lot of improvements in efficiency.

2: you have no event firing the script.