Why won't my tweensize hint box script work?

function onTouch(hit)

	if hit.Parent:FindFirstChild("Humanoid") ~= nil then

		if game.Players:FindFirstChild(hit.Parent.Name) ~= nil then
		local player = game.Players:FindFirstChild(hit.Parent.Name)

			if player:FindFirstChild("PlayerGui"):FindFirstChild("ScreenGui") == nil then
			sg = Instance.new("ScreenGui")
			sg.Parent = player:FindFirstChild("PlayerGui")
			end

		if player.PlayerGui.ScreenGui:FindFirstChild("MessageBox") == nil then

		local f = Instance.new("ImageLabel")
		f.Name = "MessageBox"
		f.Position = UDim2.new(0.15, 0, 0.65, 0)
		f.Size = UDim2.new(0, 0, 0, 0)			
		f.Image = "rbxgameasset://Images/07132e13ced5b1d6acf15e5dc35cb65a"							
		f.Parent = player.PlayerGui:FindFirstChild("ScreenGui")
        f.BackgroundTransparency = 1
wait(0.2)
        f:TweenSize(UDim2.new(0.7,0, 0,170), "In" ,"Quint", 170)
        


		local m = Instance.new("TextLabel")
		m.Position = UDim2.new(0.5, 0, 0.8, 0)
		m.FontSize = "Size14"							
		m.TextColor3 = Color3.new(1,1,1)				
		m.Parent = f


-- TEXT SECTION --

-- The following will be simple enough to edit.
-- You may copy lines along with a waiting time, and edit the text/ wait time.

------------------------------------------

m.Text = "Welcome."
m.TextColor3 = Color3.new(0,1,0)
wait(3)


m.Text = "This is my game!"
m.TextColor3 = Color3.new(0,1,0)
wait(3.5)


m.Text = "Thank you."
m.TextColor3 = Color3.new(0,1,0)
wait(2)



------------------------------------------

		f:Destroy()
		end
		end
	end
end

script.Parent.Touched:connect(onTouch)

Hi! Your code was rather hard to read due to improper indenting. Please, read up on the wiki about indenting to better help your fellow scripters understand the problems.

Errors

• On line 8, there is a If Statement that is a bit confusing. Instead of using two FindFirstChilds, use only one, as you're checking for two different objects, which could both either return true or false. This is an all or nothing if statement. My correction would be,

 if player:FindFirstChild("PlayerGui") == nil then
	if player.PlayerGui:FindFirstChild('ScreenGui') == nil 
            sg = Instance.new("ScreenGui")
            sg.Parent = player:FindFirstChild("PlayerGui")
        end
end

• On line 23, the third argument in TweenSize, will force the TweenSize to occur over the span of 120 seconds. If you would like to make it happen faster, I suggest reducing it, or removing the number altogether, as the default time is 1 second.

Tips

• When using FindFirstChild in an if statement, you no longer need to use that, you can simply refer to it. I.e.

if player.PlayerGui:FindFirstChild('Batman') then
	player.PlayerGui.Batman:Destroy()
end
--As opposed to
if player.PlayerGui:FindFirstChild('Batman') then
	player.PlayerGui:FindFirstChild('Batman'):Destroy()
end

• When checking the validity of an instance, you do not need to use ~= nil as simply typing player.Character:FindFirstChild('Humanoid') will check the validity.

If my answer helped, please accept my answer.

Happy scripting!