but it seems that doesn´t work, someone could give me a hand?
Going on from the above, if you want to add custom files, never put sound files you want to use directly in the sound folder (garrysmod/sound), because chances are, something may already exist. You need to make a new sound folder in my addon (garrysmod/addons/apple_join_disconnect_warning/sound/NEWFOLDERNAME (and be creative)), and put the sound files in there. After that, in the sv_player.lua you need to put this line resource.AddFile("") under the AddCSLuaFile( "cl_player.lua" ), and for the resource line, you need to add the directory of the new sound ( resource.AddFile("sound/NEWFOLDERNAME/soundfile.mp3") ), and then also change the surface.PlaySound("") in cl_player.lua, and that will all work.