Studio Glitch Help with Music and Sound Audios?

Random numbers are generated using a seed. By changing this seed, you can change the numbers generated. In order to change it, you'll need math.randomseed:

print('ran')
local musicholder = script.Parent
math.randomseed(tick());

local songList = {
	musicholder:WaitForChild('CW'),
	musicholder:WaitForChild('DeckDubstep'),
	musicholder:WaitForChild('EhDe'),
	musicholder:WaitForChild('JayKode'),
	musicholder:WaitForChild('Ookay'),
	musicholder:WaitForChild('SantaComes'),
	musicholder:WaitForChild('XmasToMe'),
	--musicholder:WaitForChild('Song'),
	--musicholder:WaitForChild('Song'),
	--musicholder:WaitForChild('Song')
	-- we wait for each song
	-- add the rest of the songs to this list
}
local songCount = #songList -- this returns the number of items in the table above so we only change as little code as possible when adding songs

while true do
	wait(3)
	local songNum = math.random(1, songCount) -- gets a random number in the range of the number of songs
	print(songNum)
	songList[songNum]:Play() -- we access the sound in the table and play it
	songList[songNum].Ended:Wait() -- we wait until the song has finished then play anther song
end

We use tick because tick is a function which returns the amount of time since the UNIX epoch. Since time is always changing, we can be sure that it will be a different number each time the game runs.

As an added measure, you can make sure you're choosing a different song than the song that just played easily:

print('ran')
local musicholder = script.Parent
math.randomseed(tick());

local songList = {
	musicholder:WaitForChild('CW'),
	musicholder:WaitForChild('DeckDubstep'),
	musicholder:WaitForChild('EhDe'),
	musicholder:WaitForChild('JayKode'),
	musicholder:WaitForChild('Ookay'),
	musicholder:WaitForChild('SantaComes'),
	musicholder:WaitForChild('XmasToMe'),
	--musicholder:WaitForChild('Song'),
	--musicholder:WaitForChild('Song'),
	--musicholder:WaitForChild('Song')
	-- we wait for each song
	-- add the rest of the songs to this list
}
local songCount = #songList -- this returns the number of items in the table above so we only change as little code as possible when adding songs
local played = {}; --// Create a table for played songs.

while true do
	wait(3)
	local songNum = math.random(1, songCount) -- gets a random number in the range of the number of songs

	if played[songNum] then --// Check if the song has been played.
		repeat songNum = math.random(songCount) until not played[songNum];
		--// Choose a new song.
	end;
	played[songNum] = true; --// Record that this song has been played.
	if #played == songCount then
		played = {}; --// If all of them have been played, reset the table.
	end;

	print(songNum)
	songList[songNum]:Play() -- we access the sound in the table and play it
	songList[songNum].Ended:Wait() -- we wait until the song has finished then play anther song
end

Hope this helped.

PS: I did it for you this time, but in the future please be sure to properly indent your code; this makes it easier to read for anyone trying to help you out.