How do I make a door open by clicking it?

This would be very complex just to open a door.... You could use a loop, and CFrame though. Like you could rotate it +0.001 1000 times when it's clicked using CFrame. I really have never done this before, but here's how you would do the loop:

for i = 1,1000 -- change 1000 to however many times you want this to run
--CFrame code
end

And to make it fire on click, you will have to insert a ClickDetector inside the brick, and put this script inside the brick:

script.Parent.ClickDetector.MouseClick:connect(function()
    -- loop and CFrame code in here
end)

You can use the above answer or you could make another door but Transparency 1 and CanCollide false, then make a script that when you click the Door the Door you clicked goes Transparency 1 and CanCollide false and the other Door Transparency 0 and CanCollide true, then do a wait() command and then make it so does the other Door goes Transparency 1 and CanCollide false and the Door that you click on Transparency 0 and CanCollide true, also you need to add a ClickDetector in the Door that has the script and it disables when the Door is Transparency 1.