Setting
The Setting wiki or 'namespace' is used to describe the setting of your game. It is a wiki which describes the world (or worlds), locations, people in it, as well as many other details like ships, customs, laws, factions, nations, etc. Just like wikipedia, it has pages for each one, which provides description and background information to the players and reminders and inspiration for the storyteller.
This help page describes how to write an effective Setting wiki which is useful both for the storyteller (or storytellers) and the players. To learn the technical aspects of how to create and edit pages, see the 'basics' section in the Wiki Help Index.
Special Note: All players can see the Setting wiki. Secret DM information should not be listed here
World building or 'What pages to include'
If you are a storyteller just starting out with a new game, the Setting wiki can be an excellent place for world building. You can easily keep notes, track changes you've made (and revert them if you change your mind!) and automatically generate overviews to help you put everything together.
If you use the top-down approach to world building, designing the big lines of your world before looking at the details, you can create pages for the planet or planets that your game takes place on, the biggest factions or nation states and the races, cultures and religions that fill your world.
You might want to add pages for rulers and the people in power, major locations, important legends and historical events and figures — like the founders of nations and large wars that helped shape the world as it is today.
If you use the bottom-up approach, designing the most immediately visible details that players interact with first and then expanding out to the wider world, you can create pages for the starting village, the key NPCs there like the mayor, the innkeeper and the merchant and the sheriff, as well as important locations in the area like the nearby temple ruins, the rat-infested tavern and the fortified farm half an hours walk down the road.
You might also want to add pages for local customs and legends, the closest city or neighboring town, the trade caravan that visits every month and that crazy old wizard who lives a tower out in the swamps.
Most storytellers do a little bit of both, giving a generic overview of the larger world, while providing more detail for the local environment.
Use during play
Usually, players will learn new details during their exploration: in some cases, these are discoveries of previously unknown secrets like how Mayor Cornelius is actually a polymorphed Lamassu named Xanadu. In other cases, this could be meeting new NPCs or visiting previously undiscovered planets. Sometimes new information is not so much discovered but created — like if a player marries an NPC or accidentally blows up a planet.
If the new information applies to something that is already described in the setting wiki, the page can easily be updated by the players — or the storyteller as your group might prefer — to reflect the new knowledge. If not, a new page can be created to describe the newly discovered content.
The wiki has a lot of hidden advanced features to make this easier. For example, if your character changes their name when marrying, all wiki links will automatically be updated. If you add a new planet, it will automatically appear in lists of planets. And if you find out an NPC is also operating under a different name, you can add that so both their previous name and the alias will link to the same NPC.
Tip: if someone is killed or destroyed, do not remove the page. Instead, mark them as destroyed or deceased and keep the page — that way, it becomes part of the historic record instead of disappearing.
Perspective
One important detail to keep in mind is the perspective from which information in the Setting namespace is written. For some details (how many people live in a city) this is easy. For others (like the faction page for the rebels or the empire) it might be a bit harder, especially considering what the players may or may not know.
We have found that the most effective way to use the wiki is to list information in as unbiased a form as possible. Even if it may seem to help with 'method-acting', inaccurate information tends to be more confusing than helpful to the game.
For example, if the players are part of a (secretly evil) empire, you might be tempted to describe the rebels as evil terrorists, not because they are, but because that's how empire propaganda would describe them.
Instead, try to limit yourself to the factual information about the rebels in as unbiased a way as possible and let players draw their own conclusions. If you want to add more details about what groups of people believe, try to include them with quotes or add qualifiers like 'alleged' or 'supposedly'.
Thus instead of writing "The evil terrorist rebels blew up a factory producing medicine due to their hatred for the innocent people of the empire" — which would be the empire's propaganda or at least their opinion rather than the actual truth, you could write "The rebels are implicated in the Dozi-3 pharmaceutical factory sabotage. Empire security claims the attack was motivated by rebel hatred of innocent people of the empire".