Beginner's Guide to Firefly

Firefly is set 500 years in the future, after Earth-that-was could no longer support humanity's numbers. They branched out and found new planets to live on by terraforming them.

ZOE: The border worlds -- just like the central planets, they're as close to Earth-That-Was as we could make 'em: atmosphere, gravity and such, but...
MAL: Once they're terraformed, they'll dump settlers on there with nothing but blankets and hatchets and maybe a herd. Some of them make it, some of them...

Terraforming is a process by which a planet's surface and atmosphere is altered to more resemble Earth's. The planet is then able to support transplanted human, animal, and plant life.

The core planets, those more "central" to the society and under Alliance rule, can be assumed to have been among the older planets terraformed. They have high levels of sophisticated technology and many resources to ease their way of life. Those planets farther out ('out in the black', on the rim) have rougher conditions as colonists are generally left there with few supplies and little help from the Alliance. These planets have a distinct "pioneer" culture with little technology that contrasts sharply with the way of life on the core planets.

Despite the many planets that have been colonized by humans, there has been no evidence of any alien species so far in the Firefly 'verse.

What about the Reavers?
The existance of Reavers is officially denied by the Alliance, but they are a terrifiying reality for those who live on the outer planets.

Reavers are a fictional group of humans in the television series Firefly and the movie Serenity who live on the fringes of civilized space and have become animalistic. Within the show, their existence is officially denied by the Alliance, the ruling government of humanity, but they are a harsh reality around the outer planets. Many people theorize that the Reavers are men who were driven insane by the open vastness of space at the edge of the universe. Some believe that the Reavers are "just men" who have gone too far from civilization and need help getting back, while others believe that they're something much worse. The true origin of Reavers is revealed in the Serenity movie, so I won't spoil it for you!

In the Firefly 'verse most of the territory discovered is controlled by a government known as the "Alliance". The full name of the Alliance is mentioned in the episode "Ariel" as being the "Union of Allied Planets". While the Alliance's control is absolute on the core planets, their power holds less sway on the outer rim where people can live in relative freedom.

When Earth's resources were used up and the planet could no longer support humanity, mankind left Earth-That-Was to emigrate to a new star system with "dozens of planets and hundreds of moons." The United States and China who were the two surviving world powers combined to create a central government called the Alliance. The merger also resulted in the fusion of Occidental and Oriental cultures. The Alliance originally controlled two "core" worlds, Sihnon whose population was most Chinese and Londinium who population was mostly European and European descendants.

Whedon: There is two major planets in the core.. erm, the central planets are Sihnon which is basically China and Londinium which is basically America."

The Alliance felt that all the planets in the star system should be unified under one power, but they were met with opposition who formed the Independent Faction (AKA The Browncoats). The two sides fought in a civil war called "The War Of Unification". The Independents lost and the day that the civil war ended is known as "Unification Day" or "U-Day". This day is celebrated as a holiday throughout the Alliance.

Mal: "I didn't start it! Just wanted a quiet drink."
Zoe :"Funny, sir, how you always seem to find yourself in an Alliance-friendly bar come U-day, looking for a 'quiet drink'."
Mal: See, this is another sign of your tragic space dementia, all paranoid and crotchety. Breaks the heart.

Now the Alliance theoretically controls all of the territory occupied by humanity in the star system, though they hold noticeably more sway closer to the core. Part of this may be because many be because the outer settlements don't often receive support or help from central planets.

So what's with the Western/pioneer visuals?

While terraformed planets are capable of supporting Earth's transplanted species, that is really only the first step to colonization. Unfortunately often times settlers on the outer planets, away from the core and central government, are left to fend for themselves with only minimal techno some animals and tools, receiving little if any

The Guild and Companions
The Guild is a pseudo-religious organization that trains and organizes registered Companions, who are respected professional courtesans. They hold a lot of social power and are considered among the social elite. The Guild has laws regarding the conduct of its members and the clientele. A client who disrespects or breaks these rules can be "blacklisted" and no companion will ever service them again. Companions may choose their own clients and are required to visit a a legal and respectable doctor every year for a health examination. Most companions are trained from a very young age and receive lessons in many areas, including music, psychology, fencing, and possibly martial arts.

Shepherd
A religious minister, preacher, or priest. Though not much is revealed about their activities, Shepherd Book did live in a monastery for a time before boarding Serenity.

The ship that the main characters fly is a 03 Firefly-class called "Serenity". It is a cargo vessel, no weapons or defense systems, outfitted with a photon-reaction drive (that lights up when the ship accelerates) in the rear and feet-like extenders near the bottom. The entire shape resembles a cross between a bug and a bird with the upper deck that leads to a long corridor that resembles a "neck", a large midsection, and wings that fold down like a bird's when it lands. To give the ship a bit of grace, the engine nacelles can rotate down like a VTOL aircraft.

The upper deck houses the cockpit which opens to a long corridor. The crews quarters are on a lower level off this corridor which extends all the way to the upper cargo bay catwalk. The large mid-section of Serenity is divided into two levels. The top level contains the kitchen and galley, which then lead to Serenity's engine room. The bottom level contains a small, enclosed medical area, passenger quarters, a common area, and the cargo bay.