With FE enabled ,how do you make Guis appear and disappear that are already inside the PlayerGui?

Can't find any information on it

So if you want to make a frame goes to invisible and visible in a textbutton. There is the script:

local button = script.Parent
local frame = script.Parent.Parent.Frame

button.MouseButton1Click:Connect(function()
	if frame.Visible == true then
		frame.Visible = false
	elseif frame.Visible == false then
		frame.Visible = true
	end
end)

You do it as if you would do it in a normal script, just from a local one.

If there's something on the server to make the gui pop up, you use remote events.

Anyway, the question is really vague, can you please be more specific?

If you are looking to make GUI objects such as TextButtons or Frames invisible then you would do -

local frame = Instance.new("Frame")

frame.Visible = false -- or true

If you are looking to turn the ScreenGui object invisible - which includes everything inside it, you would do -

local gui = Instance.new("ScreenGui")

gui.Enabled = false -- or true

If you are looking to Enable / Make them visible from the Server Side, then you would need to fire a RemoteEvent to either all clients or a singular client. That client would have a Local Script inside of it, which would be triggered when the RemoteEvent is fired and set the client's GUI to enabled or visible.

https://wiki.roblox.com/index.php?title=Remote_Functions_%26_Events

http://wiki.roblox.com/index.php?title=API:Class/ScreenGui

http://wiki.roblox.com/index.php?title=API:Class/Frame

More specific huh?

I have a script which should make a gui go invisible. It doesn't. It doesn't even copy the Camera script. It used to work, but now it doesn't. Everything else works apart from the gui parts and the camera script copying. Here you go:

train = game.ReplicatedStorage.C153
Camera = workspace.CurrentCamera


game.ReplicatedStorage.C153Spawn.OnServerEvent:connect(function(player)
    print("Event Received")
        player.PlayerGui.MainMenuGui.Screen.DriveFrame.Visible = false
        player.PlayerGui.MainMenuGui.Screen.Spawning.Visible = true
        player.PlayerGui.MainMenuGui.Screen.Spawning.Text = "Spawning..."
        wait(0.01)
        local clone = train:clone()
        clone.Parent = workspace
        clone:MakeJoints()
        clone.Bogies.SD_Bogie:MakeJoints()
        clone.Bogies.SD_Bogie2:MakeJoints()
        wait(1)
        player.Character.HumanoidRootPart.CFrame = CFrame.new(-2449.474, 10.174, -198.335)
        player.PlayerGui.MainMenuGui.Screen.Spawning.Visible = false
        player.PlayerGui.MainMenuGui.Screen.IntroMusic:Stop()
  script.Parent.CameraFix:clone().Parent = player.Character
end)