They are inserting it just doesnt show the Frame in the playing screen..
GUI = Instance.new("ScreenGui")
GUI.Parent = game.StarterGui
GUI.Name = "GUITEST"
GUI = true
Frame = Instance.new("Frame")
Frame.Parent = game.StarterGui.GUITEST
Frame.Name = "Holder"
Frame.Visible = true
Frame.BackgroundColor3 = ("255, 255, 255")
Frame.BorderColor3 = Vector3.new("27, 42, 53")
Frame.Size = {0,100},{0,100}
Frame.Position = {0,100},{0,100}
Frame.Transparency = 0

2 comments
Put it into playerGui
Maybe do Instance.new("Frame", GUI), and remove the 7th line