I feel like Okinawa should not need much of an introduction, as there are many more pages that have more qualifications than myself describing the rich cultural traditions and history, as well as the modern chanpuru culture and other social, economic and political situations faced here. So I will keep it short; when you visit or move here, mostly just remember that Okinawa is actually quite different from mainland Japan… there are no kimono-clad geisha or high-speed trains, meanwhile temples, shrines and architecture will have a very different look than mainland Japan, while foods and even alcohol differ from typical Japanese fare.
Okinawa is the southern-most prefecture in Japan, however it used to be an independent kingdom, the Ryukyu Kingdom, before being absorbed by Japan. They had their own language, while similar to Japanese in some aspects, it is very unique. Of course, these days, Japanese is the main language spoken everywhere here, but some places you may hear pockets of people (usually elders) speaking uchinaaguchi. Some words and phrases are used alongside Japanese (which, by the way will confuse mainland Japanese if/when you use them).
It is important to realize that the Ryukyu kingdom also had a unique culture and religion, with some similarities to Japan and China. Worship tended to be more in the form of nature worship with woods and water being sacred places, ancestor worship, and the females were spiritually superior and pure, dominated by priestesses (unlike Japanese Shintoism). Today, many Okinawans still use the lunar (Chinese) calendar to track events and ceremonies, whereas most Japanese have converted customs and rituals to the western calendar. While some events are similar to ones celebrated in Japan, they tend to be celebrated differently. There are many temples, shrines, and other utaki (sacred places) in Okinawa, but you will notice many differences from the mainland; many of my sensei have mentioned that Okinawan people in general do not tend to be very religious, though most still observe traditional customs and rituals.
Food here also tends to be different than most typical Japanese foods, though you can find many types of mainland Japanese food here in Okinawa (but it might not be quite as good as the mainland versions). Traditional Okinawa food often features pork, and while seafood is prevalent here, sushi and sashimi is usually not up to the mainland standard. Nihonshu (generically called “sake” by westerners) is not typically drunk here and there are no nihonshu breweries here. Instead, locals prefer the local distilled spirit, awamori.
People in Okinawa are very friendly and welcoming, always quick to smile. It is shima-life 島生活, “island life-style.”
While there are many beautiful beaches, it gets very cold here in winter and the beaches are closed for swimming (usually from about November to April). The temperatures might not look too chilly, but there is a biting north wind in winter, and some of the days are grey and cloudy, perhaps even a cold rain if you are unlucky. You will need a coat and long sleeves… it just is not t-shirt and slippahs weather year-round, although you will see the occasional stubborn westerner (presumably from somewhere horrendously cold like North Dakota) trying to do just this thing. That being said, obviously the average temperatures are more comfortable than mainland Japan, but do not expect year-round tropical paradise– anime has probably lied to you about what Okinawa is really like. The tourism board loves to show all the pictures from the middle of summer– they tend to leave out the winter pictures. Also, some of the nicest beaches are not on the Okinawa mainland, most are on the outer islands, so when you see those perfect clear waters and white sandy beach… you probably need to ferry or fly to get there from the main island.
The last thing to keep in mind is transportation. Okinawa does not have a train or subway system, though there is a monorail from the airport to Shuri. There are public buses, but they do not tend to run all that often so it is important to know the schedule. Having a car is the best mode of transport here.