Say you have a variable, called 'sound' for the sake of argument. If it is prefixed with 'global.', that means it's a variable that any object in the game can read. Usually variables are restricted to the object they're created in; global variables aren't restricted to one object and are persistant even if you destroy objects, change rooms etc. They are perfect for letting the game know what level or character it should load up, for example.
To use that code, do the following:
1) Open My Computer, find the folder with the game in. If there isn't one, make a folder and drop the GML file in.
2) Create a new folder, call it soundfiles, or whatever you want it to be.
3) Place all your music files in there, preferably using some sort of abbreviated system to name them, for ease (ghz_act1 for Green Hill Zone act 1, say).
4) To load that sound into the game, you would write:
global.level_music=sound_add(working_directory+"\soundfiles\ghz_act1.mp3",3,0);[/CODE] You need the speech marks in there, so the game knows it is looking at a string of text, and 'working_directory' means it will look in the folder the game is stored in. The last few numbers simply relate to what type of sound it is. When you load the music for the level, remember that most of the time it'll slow the game down badly for a moment; you may want to consider having a loading screen that stays up for a few seconds, in which you use that code to load the right music for the upcoming level; that'll give it time to get the inevitable slowdown out of the way.