How do I use Datastore to make a saving hat inventory?

Use something like this:

local DSS = game:GetService("DataStoreService")
local datastore = DSS:GetDataStore("GeneralSaveData", "Players")

function generateDataKey(player)
    local ret = "uid_" .. player.userId
    return ret
end

function generateDataTable(player)
    local dataTable = {
        Points = player.leaderstats.Points.Value,
        Wins = player.leaderstats.Wins.Value
    }
    return dataTable
end

function saveDataForPlayer(player)
    local key = generateDataKey(player)
    local data = generateDataTable(player)
    datastore:SetAsync(key, data)
end

game.Players.PlayerAdded:connect(function(player)
player:WaitForDataReady()
end)

game.Players.PlayerRemoving:connect(function(player)
player:WaitForDataReady()
end)

game.OnClose = function()
    wait(30)
end

You may have to edit it for your purposes. Hope this helps :)