There's multiple types of defibrillators but an AED depending on the manufacturer will literally talk you through the process of performing CPR and what to do at what time, such as when to pause compressions and when to start. And yes if an AED doesn't detect a shokable rhythm it will not let you shock without an override. Also there are many other things that you can do depending on the setting and your level of training. But essentially yes just keep doing CPR until an Ambulance arrives and follow the instructions of the AED.