DODECASTRATUM
Albus explains what Dodecastratum is.
Dodecastratum is the land mass that the players of SEED spawn on in UV-00282-1. The players each receive a corner of the land mass, and - in the game that takes place in PROLEGOMENON - this land mass has twelve points, one for each physical player.
Each corner of the land mass has its own quest associated with it for the player to complete before they're allowed access to the center of the land mass, where The Light is located. These corners have different biomes and societies living in these areas, which don't communicate with villagers from other corners until the players finish their quests. These villagers are the source of smaller quests that can be done to get materials or crafting recipies for items that will help them in accomplishing their main quest.
After The Light is claimed, Dodecastratum becomes a full-fledged universe, though the appearance and function of the universe changes depending on which player claimed The Light.
The amount of corners a land has is determined by the number of players, as Dodeca- means twelve, and -stratum means layers of rock or soil (literally 'twelve land'). Thus, the land that the mimeo players spawned on in their game had eight players, and presumably would have been called Octostratum.
THE LIGHT
Albus, Olivia, and Yua Matsuo inspect The Light.
The Light, or The Light (as it is always stylized as bolded black text), is the final objective when playing SEED. Each player's goal is to finish their quests in their corners of the land, and then proceed to the center, where The Light is held in a large computer that controls various aspects of the game (such as enemy spawns, Olivia and Albus, weather, etc...).
Upon claiming The Light, the player's powers from their Delegation are boosted significantly, and they are considered the winner of the game. In most games of SEED, the players need to kill each other first in order to win, which leads to gambling among the game's audience.
In PROLEGOMENON, The Light spawns strangely, described as flickering. Albus and Olivia warn that claiming it may be devastating to a player, hurting them enough to make them wish to die. This becomes a major issue in this session, as failure to claim The Light in a year's time from starting the game leads to the destruction of the game session and everything inside.
For the mimeo's session, The Light doesn't spawn at all, due to the illegal status of the session.
QUESTS
Each corner of Dodecastratum holds a quest for the players to finish before they're granted access to the center of Dodecastratum. While they vary, most of the quests involve requiring the player to utilize their abilities granted through their Delegation.
It is unknown what the quests for the mimeo players were, as this is never discussed. However, each player's quest is available on their individual pages.
VILLAGERS
Villagers come with each corner of Dodecastratum, and are the primary NPCs that exist in the world. They are different species depending on which area of the world they spawn in, though this is added by Cherry Thaxton's modifications to the game, not by the game itself. This also means the villagers are colorful animals, akin to Animal Crossing, which is not typical behavior.
As time goes on, it becomes evident the villagers have some level of self-awareness, granted by the same programming issues that give Olivia and Albus sentience.
Each villager is listed on the website.