You pick a god's name and power, and must serve them forever, as you have immortality in return. They can use their powers for whatever they please, since they're gods, and if they ask for something, you must give it to them. Thunder sounds will be heard if you mess up, and if you are unsuitable, you lose your immortality and eventually die. Or, you can choose to become the god you chose, after naming their power, but you can choose the name for it to call you anyway, and you are served instead.