Click to Open GUI

Local Script

local part = game.Workspace.Shop.Sign
local click = part.ClickDetector
local frame = script.Parent
local closeButton = frame.TextButton

frame.Visible = false

local Players = game:GetService('Players')
local player = Players.LocalPlayer

local function openShop()
    frame.Visible = true
    player.Character.Humanoid.WalkSpeed = 0
end

local function closeShop()
    frame.Visible = false
    player.Character.Humanoid.WalkSpeed = 16
end

click.MouseClick:Connect(openShop)
closeButton.MouseButton1Click:Connect(closeShop)