"make leaderstats and datastore for coins, save and load player coins. give players 5 coins every time they progress a stage. show a ui notifcation for a few seconds when a player gains coins. add detailed comments, instructions and description"

-- server script (ServerScriptService) 
local DataStoreService = game:GetService("DataStoreService")
local coinDataStore = DataStoreService:GetDataStore("CoinData")
local Players = game:GetService("Players")

-- Function to save player coins
local function saveCoins(player)
    local success, err = pcall(function()
        local coins = player.leaderstats.Coins.Value
        coinDataStore:SetAsync(player.UserId, coins)
    end)
    if not success then
        warn("Failed to save coins for player: " .. player.Name)
    end
end

-- Function to load player coins
local function loadCoins(player)
    local success, coins = pcall(function()
        return coinDataStore:GetAsync(player.UserId)
    end)
    if success then
        return coins
    else
        warn("Failed to load coins for player: " .. player.Name)
        return nil
    end
end

-- Function to setup leaderstats and load coins
local function onPlayerAdded(player)
    local leaderstats = Instance.new("Folder")
    leaderstats.Name = "leaderstats"
    leaderstats.Parent = player

local coins = Instance.new("IntValue")
    coins.Name = "Coins"
    coins.Parent = leaderstats

local savedCoins = loadCoins(player)
    if savedCoins then
        coins.Value = savedCoins
    else
        coins.Value = 0
    end

player.CharacterAdded:Connect(function(character)
        character:WaitForChild("Humanoid").Died:Connect(function()
            saveCoins(player)
        end)
    end)
end

-- Function to handle player stage progression
local function onStageProgressed(player)
    player.leaderstats.Coins.Value = player.leaderstats.Coins.Value + 5

-- UI notification script
    local notification = Instance.new("RemoteEvent")
    notification.Name = "CoinNotification"
    notification.Parent = player
    notification:FireClient(player, "You earned 5 coins!")
    wait(3)
    notification:Destroy()
end

-- Connect player added and stage progression events
Players.PlayerAdded:Connect(onPlayerAdded)
game.ReplicatedStorage.StageProgressed.OnServerEvent:Connect(onStageProgressed)

-- local script (StarterGui) 
local player = game.Players.LocalPlayer
local notificationEvent = player:WaitForChild("CoinNotification")

local function showNotification(text)
    local screenGui = Instance.new("ScreenGui")
    screenGui.Parent = player.PlayerGui

local notificationFrame = Instance.new("Frame")
    notificationFrame.Size = UDim2.new(0.3, 0, 0.1, 0)
    notificationFrame.Position = UDim2.new(0.5, 0, 0.9, 0)
    notificationFrame.AnchorPoint = Vector2.new(0.5, 0.5)
    notificationFrame.BackgroundColor3 = Color3.fromRGB(50, 50, 50)
    notificationFrame.BorderSizePixel = 0
    notificationFrame.Parent = screenGui

local notificationText = Instance.new("TextLabel")
    notificationText.Size = UDim2.new(1, 0, 1, 0)
    notificationText.BackgroundTransparency = 1
    notificationText.Text = text
    notificationText.TextColor3 = Color3.fromRGB(255, 255, 255)
    notificationText.Font = Enum.Font.SourceSans
    notificationText.TextScaled = true
    notificationText.Parent = notificationFrame

wait(3)
    screenGui:Destroy()
end

notificationEvent.OnClientEvent:Connect(showNotification)