How to save leaderboard points?

I've tried looking online, youtube tutorials, etc. but none of the ones I found worked. Here's one of the codes that I made, similar to the online ones.
local DataStoreService = game:GetService("DataStoreService") local DataStore = DataStoreService:GetDataStore("BucksStats")

game.Players.PlayerAdded:Connect(function(player)

local leaderstats = Instance.new("Folder") leaderstats.Name = "leaderstats" leaderstats.Parent = player

local Bucks = Instance.new("StringValue")
Bucks.Name  = "Bucks"
Bucks.Parent = leaderstats
Bucks.Value = DataStore:GetAsync(player.UserId) or 0

end)

game.Players.PlayerRemoving:Connect(function(player) DataStore:SetAsync(player.UserId, player.leaderstats.Bucks.Value) end)

I used a regular (not module or local script) in ServerScriptService. Tested it, did the command :change OmegaNuker Cash 2, then rejoined the game, but I then had 0 Cash. I was expecting it to be 2 cash, but it didn't work that way.

I see critical flaws with your data. First of all, you're not using pcall. pcall is designed to catch errors and is very useful for situations such as Datastores. Also, it is recommended (by roblox) that you use game:BindToClose(), game:BindToClose() allows you to run code. After 30 seconds, it will shut down, regardless of the code. (but it should be fast enough to save the player's data.)

local dataStoreService = game:GetService("DataStoreService")
local dataStore = dataStoreService:GetDataStore("BucksStats")
game.Players.PlayerAdded:Connect(function(player)
	local leaderstats = Instance.new("Folder")
	leaderstats.Name = "leaderstats
	leaderstats.Parent = player

	local bucks = Instance.new("IntValue") --If you're using numbers, it is recommend that you use an IntValue instead.
	bucks.Name = "Bucks"
	bucks.Parent = leaderstats --You need to parent it to leaderstats, not the player.

	local data --You should add it in order to get the data. default variables are always equal to nil.
	local success, errorMessage = pcall(function() --If you did not add pcall, it would break your script.
		data = dataStore:GetAsync(player.UserId) or 0
	end)
	if success then --Alternative: If success == true
		print("Data found!") --You should add prints in order to troubleshoot.
		bucks.Value = data
	else
		warn("Error while getting data: "..errorMessage) --This gives some sort of code if there is any problem.
	end
end)

game.Players.PlayerRemoving:Connect(function(player)
	local success, errorMessage = pcall(function()
		dataStore:SetAsync(player.UserId, player.leaderstats.Bucks.Value)
	end)
	if success then
		print("Data saved and player left") --You should add some sort of different message, in order to not confuse it between others.
	else
		warn("Error while saving data: "..errorMessage)
	end
end)

game:BindToClose(function()
	for _, player in pairs(game.Players:GetPlayers()) do --This gets the player in the server.
		local success, errorMessage = pcall(function()
			dataStore:SetAsync(player.UserId,player.leaderstats.Bucks.Value)
		end)
		if success then
			print("Data saved and game closed")
		else
			warn("Error while saving data: "..errorMessage)
		end
	end
end)