How to randomize what a button does and also add a wait?

Hello! I'm just learning how to script. Someone helped me while I was making a script for a button that would change the song playing every time it was pressed, and I learned quite a lot from that!! I'm now trying to modify the script so that it randomizes what song plays when the button is pressed, and also make it so the button can only be pressed every 30 seconds.

Here is my script after i've recieved help from the accepted answer below!!

local songs = {
    "http://www.roblox.com/asset/?id=2206587324",
    "http://www.roblox.com/asset/?id=4737555180",
    "http://www.roblox.com/asset/?id=2231782710",
    "http://www.roblox.com/asset/?id=2538961789"
}
local songLength = #songs               
local Sound = script.Parent.Parent.Sound    
local CD = script.Parent
local randomGenerator = Random.new()                                             
local selected = 0 
Sound.Pitch = 1 
Sound.Volume = 3
Sound.Name = "Player"     
song1 = "http://www.roblox.com/asset/?id=2538961789" --paste last song id here
Sound.SoundId = song1 
Sound:play()
enabled = true              
CD.MouseClick:Connect(function()
	if not enabled then
		return
	end
	enabled = false              
    selected = randomGenerator:NextInteger(1, #songs)                      
    local chosen = selected%#songs      
    if chosen == 0 then                 
	chosen = #songs
    end 
	print(chosen)
    Sound.SoundId = songs[chosen]       
	Sound:Play()
	Sound.Looped = true
	wait(30)
	enabled = true
    end)

Here is the original script:

local songs = {
    "http://www.roblox.com/asset/?id=2206587324",
    "http://www.roblox.com/asset/?id=4737555180",
    "http://www.roblox.com/asset/?id=2231782710",
    "http://www.roblox.com/asset/?id=2538961789"
}
local songLength = #songs               
local Sound = script.Parent.Parent.Sound    
local CD = script.Parent                                             
local selected = 0 
Sound.Pitch = 1 
Sound.Volume = 3
Sound.Name = "Player"     
song1 = "http://www.roblox.com/asset/?id=2538961789" --paste last song id here
Sound.SoundId = song1 
Sound:play()              
CD.MouseClick:Connect(function()            
    selected += 1                       
    local chosen = selected%#songs      
    if chosen == 0 then                 
	chosen = #songs
    end
    print(chosen)
    Sound.SoundId = songs[chosen]       
	Sound:Play()
	Sound.Looped = true
    end)

here is my modified version that doesn't work :( the output states: (Workspace.Model.Button.ClickDetector.Script:19: attempt to perform arithmetic (mod) on table and number) --I sort of understand this, but I don't know how else to make it Random

local songs = {
    "http://www.roblox.com/asset/?id=2206587324",
    "http://www.roblox.com/asset/?id=4737555180",
    "http://www.roblox.com/asset/?id=2231782710",
    "http://www.roblox.com/asset/?id=2538961789"
}
local songLength = #songs               
local Sound = script.Parent.Parent.Sound    
local CD = script.Parent                                             
local selected = 0 
Sound.Pitch = 1 
Sound.Volume = 3
Sound.Name = "Player"     
song1 = "http://www.roblox.com/asset/?id=2538961789" --paste last song id here
Sound.SoundId = song1 
Sound:play()              
CD.MouseClick:Connect(function()            
    selected = Random --changed += 1 to Random but it just makes the button not work...                       
    local chosen = selected%#songs      
    if chosen == 0 then                 
	chosen = #songs
    end
    print(chosen)
    Sound.SoundId = songs[chosen]       
	Sound:Play()
	Sound.Looped = true
	wait(30) --added wait but doesnt do anything
    end)