How to share variables between scripts and change them?

Hey guys, i'm new to scripting in Roblox Studio, so I hope you could help me with a problem... So, i have a ModuleScript and i have a variable called "Buttonleft" in it. My idea is to crate a game that, when 4 buttons are pressed (not necessarily at the same time), a door is opened (like Dead by Daylight and the generators)... My problem is, when i press a button, the variable Buttonleft (wich is a int variable equal to 0) increases the value, becoming Buttonleft = 1. So, i need to everytime a player presses a button, this variable increases, but it is not working. The ModuleScript keep saying that Buttonleft = 1 when i press more than 1 button, when it should be printing "Buttonleft = 2" "Buttonleft = 3" and on and on... But it just doesn't work :/ Here's my codes:

ModuleScript

local Buttons = { Buttonleft = 0 }
return Buttons

Buttons Script

clickquantity = 5
Buttons = require(game.ServerScriptService.Buttons)

function clickbutton()
	workspace.Painel2.SurfaceGui.TextLabel.Text = clickquantity .. " Click's left"
	clickquantity = clickquantity - 1
	if clickquantity == 0 then
		workspace.Painel2.SurfaceGui.TextLabel.Text = "Finished Button"
		Buttleft = Buttons.Buttonleft
		Buttleft = Buttleft + 1
		print(Buttleft)
	elseif clickquantity < 0 then
		workspace.Painel2.SurfaceGui.TextLabel.Text = "Finished Button"
	end 
end

game.Workspace.Button2.ClickDetector.MouseClick:Connect(clickbutton)

Can you please help me? Thanks :)

It would appear you messed up pass by value and pass by reference. On line 9 and 10, tables will pass by reference but most primitive types will not. You must write out Buttons.Buttonleft = Buttons.Buttonleft + 1

As primitive values will copy instead of just passing the location address. You can play around with this a bit in some functional environments:

function a(someTable)
	print(someTable)
end

local myTable = {}
print(myTable)
a(myTable)

--Both print the same thing.

function b(someNumber)
	someNumber = someNumber+1
	print(someNumber)
end

local myNumber = 4
print(myNumber+1) -->5
b(myNumber)-->5
print(myNumber)-->4

Similarly these rules are the same for the contents of a table.

function c(somethingInATable)
	--I'm going to assume somethingInATable is a number which is bad practice
	--but this is demonstration.
	somethingInATable = somethingInATable+1
	print(somethingInATable)
end

local myTable2 = {a = 1,b = 2,c = 3,d = 4}

c(myTable2.d)-->5
print(myTable2.d)-->4