PlayerGui

The PlayerGui object is a container that holds a player's user GUI. If a ScreenGui is a descendant of a PlayerGui, then any GuiObject inside of the ScreenGui will be drawn to the player's screen. Any LocalScript will run as soon as it is inserted into a PlayerGui.

When a player first joins a game, their PlayerGui is automatically inserted into their Player object. When the player's Player.Character spawns for the first time all of the contents of StarterGui are automatically copied into the player's PlayerGui. Note that if Players.CharacterAutoLoads is set to false the character will not spawn and StarterGui contents will not be copied until Player:LoadCharacter() is called. If StarterGui.ResetPlayerGuiOnSpawn is set to true then every time the player's character respawns all of the contents of that player's PlayerGui is cleared and replaced with the contents of StarterGui.

-- Accessing PlayerGui from a LocalScript:
game:GetService('Players').LocalPlayer:WaitForChild('PlayerGui')