How do I make someones walk speed zero?

I was trying to make a game and i'm trying to make the person walk speed when they are in a certain point in a game or when text appears on screen at a certain point. By the way i'm pretty nooby at scripting so forgive me if I make simple mistakes.

I also put the local script into StarterPlayer so if I also got that wrong then please forgive me.

if game.StarterGui.Intro.Frame.Visible == true then script.Parent.CharacterWalkSpeed = 0 end

Inputting a Local Script into StarterGui will do the trick here

local plr = game.Players.LocalPlayer
local pGui = plr:WaitForChild("PlayerGui")
local char = plr.Character or plr.CharacterAdded:Wait()

if pGui.ScreenGui.Frame.Visible == true then -- the check you please
	char.Humanoid.WalkSpeed = 0 -- the speed you please
end -- closing the if statement