Not calling a function?

No, theses function will never run until you call them here a little exemple.

function runningAFunction()
    print("This function is running yay !")
end

runningAFunction()--It will run the function, thats mean you'll see in your output ~"This function is running yay !~

you can also call a function like that

local aFunction = function()
    print("Another function is running :D !")
end

aFunction()--It will run the function, thats mean you'll see in your output ~"Another function is running :D !~

you can put some Settings like that

function sum(a, b)
    return a + b --without return when you're running the function and if you're trying to print the function it'll print a nothing
end

print(sum(5, 5))--It'll print 10 because 5 + 5 is 10 hehe

with return you can return more than one thing like:

function sum(a, b)
    return a + b, "the second object" --without return when you're running the function and if you're trying to print the function it'll print a nothing
end

local theSum, theString = sum(5, 5)

now if you you print like this:

print(theSum, theString)--you'll see in your output 10 and the second object

and now the final result will look like this

function sum(a, b)
    return a + b, "the second object"
end

local theSum, theString = sum(5, 5)
print(theSum, theString)--you'll see in your output 10 and the second object

Now your code here:

local door = script.Parent
local oppened = false -- open the door if  the door is closed or close the door if it's openned
local debounce = false--added debounce for be sure It will not spam the functions

function open()
    oppened = true
    -- This function will open the door.
    door.CanCollide = false -- Make players able to walk through the door.

    for transparency = 0, 1, .1 do
        door.Transparency = transparency
        wait(.1)
    end
end

function close()
    oppened = false
    -- This function will close the door.
    for transparency = 1, 0, -.1 do
        door.Transparency = transparency
        wait(.1)
    end

    door.CanCollide = true -- Make players unable to walk through the door.
end

door.Touched:connect(function()
    if debounce then return end
    debounce = true
    if not oppened then
        open()
    else
        close()
    end
    wait(1)--wait 1 seconde before you can run the other function
    debounce = false
end)

Thats all I know If I don't forget one thing, enjoy !