Script is working when I run it, but not when I play it. Do I need a function?

I am making an intro sequence for my game. The script is supposed to create a frame which fades from black to another gui. Here's the code:

--Fade in parts--
local size = UDim2.new(0, 1920,0, 1080)
local pos = UDim2.new(0, 0,0, 0)
local color = Color3.new(0,0,0)
local ScreenGui = Instance.new("ScreenGui",game.StarterGui)
local frame = Instance.new("Frame",ScreenGui)
frame.Size = size
frame.Position = pos
frame.BackgroundColor3=color

--Fade in--
wait(1)
for i = 0, 1, 0.025 do
    frame.BackgroundTransparency = i
    wait(.025)
end

Do I need to add a onPlayerAdded function? I am quite new to this whole scripting thing.