how to make level / exp script

--=========This Script Is Originaly Produced By==============
--============== Rigby#9052 ========================
--==============Used & Tested by:(JUB0T)==============
--Dont change the original owners

function onXPChanged(player, XP, level)
	if XP.Value>=level.Value * 10 then
		XP.Value = XP.Value - level.Value * 30
		level.Value = level.Value + 1
	end
end

function onLevelUp(player, XP, level)
	if player.Character~=nil then
		for i = 1,5 do
			local fireworks = Instance.new("Part")
			fireworks.Shape = 0
			fireworks.formFactor = "Symmetric"
			fireworks.Size = Vector3.new(1,1,1)
			fireworks.BrickColor = BrickColor.Random()
			fireworks.CFrame = player.Character.Head.CFrame + Vector3.new(0,2,0)
			fireworks.Parent = game.Workspace
			game:GetService("Debris"):AddItem(fireworks, 2)
			fireworks.Velocity = Vector3.new(math.random(-30,30),math.random(-30,30),math.random(-30,30))
		end
	end
	local m = Instance.new("Hint")
	m.Parent = game.Workspace
	m.Text = player.Name .. " has leveled up!"
	wait(3)
	m.Parent = nil
end

function onPlayerRespawned(player)
	wait(5)
	player.Character.Humanoid.Health = player.leaderstats.Level * 50
	player.Character.Humanoid.MaxHealth = player.leaderstats.Level * 50
--[[
	local stuff = player.Backpack:GetChildren()
	wait(5)
	for i = 1,#stuff do
		local name = stuff[i].Name
		if game.Starterpack:findFirstChild(name)==nil then
			stuff[i]:Clone().Parent = player.Backpack
		end
	end
--]]
end

function onPlayerEntered(newPlayer)
	local stats = Instance.new("IntValue")
	stats.Name = "leaderstats"

	local xp = Instance.new("IntValue")
	xp.Name = "XP"
	xp.Value = 0
	
	local level = Instance.new("IntValue")
	level.Name = "Lvl"
	level.Value = 1

	local c = Instance.new("IntValue")
	c.Name = "Gold"
	c.Value = 0

	xp.Parent = stats
	level.Parent = stats
	c.Parent = stats

	stats.Parent = newPlayer

	xp.Changed:connect(function() onXPChanged(newPlayer, xp, level) end)
	level.Changed:connect(function() onLevelUp(newPlayer, xp, level) end)

	newPlayer.Changed:connect(function (property)
		if (property == "Character") then
			onPlayerRespawned(newPlayer)
		end
	end)
end

game.Players.ChildAdded:connect(onPlayerEntered)