There are doubtless regional variations but the basic recipe consists of several layers made up of meat (for example, chunks of lamb) covered with chopped onions then sliced potatoes. As many layers can be added as will fit in the pot.
Flavour can be enhanced with seasoning - salt and pepper would be the most traditional - and any other ingredients available in the kitchen. Some stock could be added but a well sealed pot on a low heat will probably have enough moisture within the meat, onion and potatoes, enhancing and mingling the flavours rather than washing them away.