Oh boy... haven't you already messed around a little bit with CombiWave? Try pressing '1', '2' or '3' on your keyboard. These are so called hot keys. That's basically what Combiwave is all about: play multiple audiofiles by pressing a single key on your standard computer keyboard. Maybe you should learn more about hot keys...
Another useful option: a selected slot (blue frame by default) can be started (and stopped) by pressing 'Enter'.
A special feature is the Cue Control which is an additional window. The currently selected slot can be started by clicking '> Play' in this window. To enable the Cue Control click 'View' in the menu and check 'Cue Control'.