why does a script to show a gui in game not work? What should I do? Nothing appears.

script not working: script.Parent.ClickDetector.MouseClick:Connect(function() game.Players.LocalPlayer.PlayerGui.ScreenGui.Frame.Visible = true end)

when i click a part it should appear but it does not. Any fixes?

Try using instance:WaitForChild(): https://developer.roblox.com/en-us/api-reference/function/Instance/WaitForChild

It is not a local script. Try this script. Also use a code block when typing your code.

script.Parent.ClickDetector.MouseClick:Connect(function(player) player.PlayerGui.ScreenGui.Frame.Visible = true
end)