if player click button then +500cash - How to make it ?

if player click button then +500cash - How to make it ? button = script.Parent

If you wish to SAVE these stats, you must use a remote event to trigger the server to change them.

Local Script:

local Button = script.Parent
local Remote = Instance.new("RemoteEvent")

Remote.Parent = game:GetService("ReplicatedStorage")
Remote.Name = "AddMoney"

local function FireRemote()
  Remote:FireServer()
end

local function DescAdded(Inst)
   if Inst.Name == "Loaded" then
       Button.MouseButton1Down:Connect(FireRemote)
   end
end

Remote.DescendantAdded:Connect(DescAdded)

Server Script:

( PUT THIS IN SERVERSCRIPTSERVICE )

local ReplicatedStorage = game:GetService("ReplicatedStorage")
local MoneyRemote = ReplicatedStorage:WaitForChild("AddMoney")
local Loaded = Instance.new("BoolValue")

Loaded.Name = "Loaded"
Loaded.Parent = MoneyRemote

MoneyRemote.OnServerEvent:Connect(function(Player)
  local MoneyValue = Player["leaderstats"]["YOURVALUENAME"] -- change to your money value name

  MoneyValue.Value = MoneyValue.Value + 500
end)

RemoteEvents Documentation

FireServer Documenation

OnServerEvent Documentation