Delve into a cavern floor by floor. Courage is the resource that lets you keep going, health is the one that runs out, and the combat happens on its own once you have walked into something. Upgrades raise attack, defense, attack speed and move speed, and the floors count up ten enemies at a time.
Reach floor six and you can prestige, losing everything for prestige points and half a research per reset. The author calls it a prototype made in a few days and version 0.0.8 agrees with them, so expect an idea rather than a finished game. There is a real half hour in it before you run out of new floors.