The beginning
You are a humble nomad who wanders the streets of Sayas; a city in the afterlife. You have not yet been chosen to go to The Elysian Fields or Tartarus, this choice is yours.
With good intentions you ask people for something to do for something to eat or a place to sleep. Sometimes people ask you to do kind and friendly things like, pickup some groceries or rescue a pet that has fallen in a well, and others ask you to do something illegal. It's up to you what quests you accept and what you don't. But keep in mind that everything you do has consequences and inflict your Karma level. With a high enough karma level you will be, in time, able to enter The Elysian Fields or when your karma goes too low, you will go to Tartarus.

Sayas -Afterlife
Sayas is the beginning of Thanatos Online, upon your death you will start your new life here. This place is seen as a Tutorial, the game concepts is explained, and you will reach a specific level here before continuing to The Elysian Fields or Tartarus.

The Elysian Fields -Heaven
When you reach enough positive karma you can enter The Elysian Fields, here you will choose your class and gain special skills and abilities.

Tartarus -Hell
When your karma level is low enough you will be able to go to Tartarus, just as in The Elysian Fields, you will choose your class and gain special skills and abilities here.

Gaia -Earth
Upon choosing your preferred class and skill-sets you can return to Gaia, to the realm of the living. You will be here most of the time preforming quests and gaining experience. You are able to return to The Elysian Fields or Tartarus at any time. The Gaians are not be able to see who you really are, to them, you are just another human minding your own business. This is also the reason why the Elysians and Tartarens can be in the same place without anyone noticing.