Can Someone Help with DataStore Script?

I'm trying to make a script that uses a script that saves the player's inventory if they leave the game. Here's what I have so far:

local ds = game:GetService("DataStoreService"):GetDataStore("tools")

game.Players.PlayerAdded:connect(function(player)
	local key = "user_" .. player.userId
	ds:UpdateAsync(key, function(old)
		old = game.Players.LocalPlayer.Backpack:GetChildren()
		if old:IsA("Tool") then
		local new = old or nil
		local tool = old:Clone()
		tool.Parent = game.Players.LocalPlayer.Backpack
		return new
		end
	end)
	
end)

I copied some of it from the wikia. I think I'm doing it all wrong. Please help!

I suggest looking over http://wiki.roblox.com/index.php?title=Data_store again and reading it properly. To do this I would make a tablewith item names in it and then you use those to access ReplicatedStorage and clone the tools into their Backpack.