I've made a gui with mute button and thing but umm i doesn't play the music?

I'm not really sure about how the structure of your codes and objects work but in order for a song to play you have to first set the SoundId in a sound instance and then use the Play() function. You don't have to use the play function. If you have checked Playing in the properties of the sound then it will play automatically.

Also, if you are sending a string that is the song id through the RemoteEvent then you should use it like so:

game.ReplicatedStorage.Events.UpdateSong.OnClientEvent:connect(function(Song)
    print(Song)
    Sound.SongId = Song
    Sound:Play()
end)

There are probably other ways to use it but without trying too much this is what I came up with.