How do i save playerstats?

You can save stats through data stores, replace the whole code of your script with this code:

local DataStoreService = game:GetService("DataStoreService")
local DataStoreVersion = 1 -- Changing this version will wipe all data of players
local DataStore = DataStoreService:GetDataStore("DataStoreV"..DataStoreVersion) -- Changing "DataStoreV" will also wipe all data of players

game.Players.PlayerAdded:Connect(function(Player)
	local Leaderstats = Instance.new("Folder",Player)
	Leaderstats.Name = "leaderstats"
	local Cash = Instance.new("IntValue",Leaderstats)
	Cash.Name = "Cash"
	local Coins = Instance.new("IntValue",Leaderstats)
	Coins.Name = "Coins"
	local Rebirths = Instance.new("IntValue",Leaderstats)
	Rebirths.Name = "Rebirths"
	local loadedcash
	local loadedcoins
	local loadedrebirths
	local success,errormessage = pcall(function()
		loadedcash = DataStore:GetAsync(Player.UserId.."-Cash")
		loadedcoins = DataStore:GetAsync(Player.UserId.."-Coins")
		loadedrebirths = DataStore:GetAsync(Player.UserId.."-Rebirths")
	end)
	if success then
		Cash.Value = loadedcash
		Coins.Value = loadedcoins
		Rebirths.Value = loadedrebirths
	else
		print("Data load encountered an error,Player Data not loaded")
		warn(errormessage)
	end
end)

game.Players.PlayerRemoving:Connect(function(Player)
	local success,errormesssage = pcall(function()
	DataStore:SetAsync(Player.UserId.."-Cash",Player.leaderstats.Cash.Value)
	DataStore:SetAsync(Player.UserId.."-Coins",Player.leaderstats.Coins.Value)
	DataStore:SetAsync(Player.UserId.."-Rebirths",Player.leaderstats.Rebirths.Value)
	end)
	if success then
		print("Data Save was successful")
	else
		print("Data Save Error Occured, Data not saved")
		warn(errormesssage)
		end
end)

The code works but you should also learn how to use data stores yourself.