Did you forget a colon? The first argument of member function GetAsync must be an Object

local module = {}

local DataStore = game:GetService("DataStoreService"):GetDataStore("M12341123231")

local StarterPounds = 0

game.Players.PlayerAdded:connect(function(player) local Stats = Instance.new('Folder', player) Stats.Name = "Stats"

local Pounds = Instance.new('NumberValue', player)
Pounds.Name = "Pounds"
Pounds.Value = StarterPounds
Pounds.Parent = Stats

local SavedPounds = DataStore.GetAsync(player.UserId..'-Pounds')
if SavedPounds == nil then
	Pounds.Value = SavedPounds
end 

end)

game.Players.PlayerRemoving:connect(function(player) local id = player.UserId local PoundsValue = player.Stats.Pounds.Value DataStore:SetAsync(id..'-Pounds', PoundsValue) end) return module

Whenever I change the first argument I get UserId isn't a valid member of Player.~~~~~~~~~~~~~~~~~

You are using the following:

DataStore.GetAsync()

You should be using the following:

DataStore:GetAsync()

GetAsync is a function, not a property, so it must be called upon with a colon rather than a period.