Sin is the beast that has been cast upon the world of Spira for them to pay for their actions for relying on Machina and using it to kill and make their lives easy.
For a thousand years summoners would go on a pilgrimage to hone their abilities as they traveled to the ruins of Zanarkand to gain the final Aeon (Summoning) in hopes of finally killing Sin and bringing an eternal calm. Though no one has done so and Sin has continued to appear after a year or two after it's defeat. The people of Spira keep hope in their hearts that one day it will be gone for good.
Greatly resembling a large island, Spira is composed of a mainland continent with several smaller islands to the east, west and south. Spira consists of many diverse climates: the tropical seaside islands of Besaid and Kilika, the temperate locales in the Mi'ihen Highroad and Mushroom Rock regions, the polar extremes of Macalania and Mt. Gagazet, the deep, mystical forests of Macalania and the arid deserts of Bikanel.
People in Spira can be seen weaving, working in shops, bars and travel agencies, playing blitzball, raising chocobos, sailing boats, managing shoopufs, working in archaeological digs, working as Mercenaries/Sphere Hunters and performing in a variety of entertainment troupes. One assumes some Spira residents fish and grow produce to supply their fellow Spirans with consumable goods.
Another form of occupation is shown in voluntary works such as the summoner/guardian pilgrimages and various religious temple work.
Spira uses gil as its official currency, but evidence dug out in the Bikanel Desert by Al Bhed expedition parties indicate it may have used gold coins in the past.
The once abundant machina is now encouraged to be shunned by Bevelle's edicts, and only the outcast race, the Al Bhed, attempt to regain some of the lost knowledge. Due to the censorship on machina, fighters who utilize magic for battle have become commonplace and in demand, and none more so than summoners, who enjoy something of a caste of their own: help and privileges are granted to them during their pilgrimage in exchange for their coming sacrifice against Sin.
Yevon (A Religion) dominates every aspect of Spiran life, spreading its teachings and acting as a benevolent protector of a much diminished world - a world where no more than forty million people live and virtually any kind of technological and social progress has been asleep for 1000 years. Yet, beneath the surface, unity of the Spiran mainland, distrust and old anger still boils deep, leading one to perhaps wonder if the various warring factions wouldn't have blown each other to smithereens without Sin's pacifying presence. Only blitzball truly unites the world around a common passion, the sport, which survived Sin's coming and which holds annual tournaments in Luca's stadium, left untouched by Sin's wrath mostly due to the Crusaders' efforts.
Ronso- The Ronso are a race of muscular, anthropomorphic feline humanoids. The Ronso tribe lives at the base of Mt. Gagazet and guard the sacred mountain fiercely. They are formidable warriors, well known for their strong sense of honor and loyalty, as well as their pride and quickness to anger.
Humans- Humans also known as Hume and Humanoid.
Al Bhed- The Al Bhed are a human tribe of technologists. Making up ten percent of the Spiran population, they are notable for their unique language and their use of machina, a technology prohibited by Yevon.
Guado- The Guado are a humanoid race that lives amongst trees, they are the protectors of Spira's afterlife, the Farplane, and the Macalania Woods. The Guado's capital city is Guadosalam, from within which they guard the entrance to the Farplane.
Hypello- The Hypello are a race of amphibian creatures. The Hypello seem not to have grasped the common pronunciation in Spira, often lisping any words with an 'S,' for example Shay (say) and Yesh (yes), converting some words into gibberish, for example Ebullibody (everybody), Inveshtitagating (investigating) Imposhibibble (impossible), as well as ending most of their sentences with a questioning tone. They are agile in the water, but are not so nimble on dry land, walking at a torpid pace.
[Your Current Story]
You wake up once again on the peaceful Island of Besaid. The Calm ended recently and since the Island has little too no Machina Sin seems to never attack it. This reason alone is what drew you to move here.