Well, firstly there's the official settings on the Planeshift website -www.planeshift.it- but these should be rewritten soon, as there are a number of inconsistancies. Secondly, there's the Jayose library ingame. There's a number of bookcases, which can be examined to find the books- for religious information, the website's probably best, although "Song of the Lemur" in the library says a little. There's also some slightly more recent and less religious history, such as the founding of Gugrontid, and information about the economy can be found in equal parts on both the website and in the library. You can also find out quite a bit about the settings from talking to NPCs (specifically Yliakum geography)- try a teacher, such as Kilas Tungst. Useful questions could be phrased like- "tell me about the winch", etc
Well, I hope you find what you're looking for.