I am trying to script an elevator door and cant get it to work. What do I do?

On your while true do loop, it opens the elevator doors then it waits 3 seconds and then closes the doors and then instantly opens them. This is probably happening so fast that you don't see it actually closing. This is the fixed version.

local door = script.Parent.Door

local function openelevator() 
    door.CanCollide = false 
    door.Transparency = .5 
    door.BrickColor = BrickColor.new("Bright green")
end

local function closeelevator()
    door.CanCollide = true
    door.Transparency = 0
    door.BrickColor = BrickColor.new("Black")
end

while true do
    openelevator()
    wait(3) -- Time to wait until doors close
    closeelevator()
    wait(2) -- Time to wait for doors to open
end