The Rebel Legion is a world-wide, charity-based Star Wars costuming club. Founded in 2000, the Rebel Legion is the sister organization of the 501st Legion and Mandalorian Mercs. While the 501st consists of Imperial ("bad guy") characters in Star Wars and the Mandalorian Mercs are Mandalorian bounty hunters, the Rebel Legion includes members of the Rebellion, Resistance, and Jedi Order ("good guys"). You can read more about the history of the Rebel Legion here.
Garrison Corellia is the West Virginia Chapter of the 501st. The 501st Legion is a world-wide organization. There are over 50 garrisons in the North American region alone. A garrison covers a large region distinguished by geography, language, or other characteristics or borders.
To join the Rebel Legion, individuals must be at least 18 years old and own an approved Rebel Legion costume. You can start the process by signing up for the Rebel Legion forums and selecting the Base for your area (Amancane Base for West Virginia). More details about joining can be found here.
The next big decision is choosing a costume. To be approved, costumes must meet certain criteria, which are governed by the Costume Standards. Choose your favorite character, one that just looks cool, or one that will be easy to make. Many members have more than one costume, so the question is which costume to make FIRST, not which costume to make.
Certain characters might have specific requirements about hair (ie. Han Solo, Princess Leia, Rey) or height (Wookiees), but body type, race, and gender typically do not matter when choosing a costume. The focus is on the costume's appearance, and not on the person. Special accommodations may be made for disabilities and religious requirements.
Armor parties are gatherings to work on costumes. They don't need to involve actual armor, so all costumes are welcome. Some armor parties have become "sewing parties." Armor parties are a chance to meet members of the Base (and maybe the local Garrison, too).
Beyond the social aspects, you can get advice and hands-on help building your costume. Many members bring tools that you might need but not own. Even if you don't need help on a costume, you can lend a hand to someone else who is building a costume, and gain valuable knowledge, both about specific costumes and general techniques.
Don't let a lack of costuming experience stop you from joining. Even if you have no costume building skills at all, you can get the help that you need to make an approvable costume. Armor parties are a great way to make both new costumes and new friends, as well as have fun with old friends.
Younger than 18 year old, but still a Star Wars fan? You can join the Galactic Academy. Kids are welcome to get their own costumes and pretend to be their favorite Star Wars characters. Unlike the Rebel Legion, 501st, and Mandalorian Mercs, the Galactic Academy does not have costume standards, an approval process, or a distinction among characters (Rebel, Imperial, or Merc). Galactic Academy costumes can be custom-made to meet the standards of the parent groups, or be bought from a store. The focus is on having fun and sharing the joy of Star Wars.