SOUND* whamm = "whamm.wav";
var whamm_handle;

These bits are definitions of the actual Sound file, and a variable which allows you to control the sound (pause, stop etc). These can be defined globally, which means anywhere outside a function/action. Its best to have them at the top of your script, or even in a seperate script if you want.

The last bit,whamm_handle = snd_loop(whamm, 100, 0);, should be called inside a function or action.