All custom sounds should be in .ogg format and placed inside the /sounds folder.
You can directly reference any sound by calling sound_get( name:string ). Then you can either play it from any script:
sound_play( sound_get( "name" ) );
or assign it to the attack grid:
set_window_value( AT_JAB, 1, AG_WINDOW_SFX, sound_get( "name" ));
You can also use any custom sound as character’s victory theme:
set_victory_theme( sound_get( "name" ) );