How do you make a loading screen when switching the game?

According to roblox wiki

Disabling Roblox's default loading screen To turn off the default loading screen, insert a LocalScript into ReplicatedFirst. ReplicatedFirst is a service that replicates Instances to the client before anything else is replicated when the game is loading. Putting a LocalScript in ReplicatedFirst guarantees this script will be the first script the client runs.

In this LocalScript RemoveDefaultLoadingScreen is called to remove the default Roblox loading screen:

game.ReplicatedFirst:RemoveDefaultLoadingScreen() Create loading screen A loading screen can use any or all of the GUI elements that Roblox provides. These elements should be parented to the LocalPlayer's PlayerGui in a local script in ReplicatedFirst. The GUI elements can either be stored in ReplicatedFirst, or can be created by the script and put immediately into the PlayerGui. The Topbar should also be made opaque to hide any geometry that might be loading behind it.

local PlayerGui = game.Players.LocalPlayer:WaitForChild("PlayerGui") PlayerGui:SetTopbarTransparency(0)

local screen = Instance.new("ScreenGui") screen.Parent = PlayerGui

local textLabel = Instance.new("TextLabel") textLabel.Text = "Loading" textLabel.Size = UDim2.new(1,0,1,0) textLabel.FontSize = Enum.FontSize.Size14 textLabel.Parent = screen Note: There is a small delay when waiting for the PlayerGui. If you hide the default loading screen before you wait for the PlayerGui to load the game will be visible for a brief moment. It is recommended to wait for the PlayerGui to load first, insert the initial screen you want to display, and then hide the default loading GUI. Hiding loading screen At some point the loading screen should be hidden when all the loading has been finished. Even if your loading screen is intended to play for longer than the actual time needed to load (for instance showing splash screens) it is still useful to know when the game is ready to be played. Functions like RequestQueueSize and IsLoaded can be used to see if content is present in the game, but these will not say if the level has rendered or not. Therefore it is best to have your loading screens wait a set amount of time scaled on how long it takes your game to initially render.