Jedi Ranks: In the days of the Galactic Republic, most prospective Jedi are recruited at a very young age—presumably before they are 8 years old, since Anakin (age 9) and Luke (around age 20) are both considered "too old" by Yoda. A young recruit is called a padawan learner (or "apprentice"). A padawan uses a blue-bladed lightsaber given to him by his "master" (teacher). Once an apprentice completes his training and overcomes an appointed challenge (the "Trials"), he becomes a true Jedi knight. A Jedi who proves himself skillful enough to train a young apprentice of his own becomes a Jedi master. After many years of service, an experienced Jedi may be granted the ultimate honor of being asked to join the Jedi Council. All Jedi (apparently even the Sith) follow the Rule of Two—a master should always have one apprentice. Although an elder master (such as Yoda) may train many apprentices throughout the years, it is always one at a time.
Midi-chlorians: These microscopic organisms dwell inside all Force-users, and possibly all intelligent life forms. It is uncertain whether or not midi-chlorians generate the Force, but it is known that those who are naturally strong with the Force have a higher natural concentration of midi-chlorians in their blood. Young Anakin Skywalker had a natural concentration of over 20,000 (which is apparently higher than any Jedi has ever had).
Rodians: These green-skinned, spikey-headed aliens have a definite leaning towards the profession of bounty hunter. Greedo was a Rodian in Jabba the Hutt’s employ.
Neimoidians: These fish-skinned, reddish-eyed aliens control the Trade Federation. The Neimoidians serve as their own ambassadors, commanders, and ship captains, but they rely on droids and alien hirelings to do their dirty work. Neimoidian battleships, carrying huge fleets of space fighters, are among the most powerful warships in the galaxy.
Sith Ranks: Presumably any Jedi who is seduced by the Dark Side can become a Sith Apprentice. After demonstrating a high degree of power, he can become a full Sith Lord. An elder Sith who takes on his own apprentice is known as a Sith Master. Every Sith fights with red-bladed lightsaber regardless of his rank. Additionally, every Sith adopts the first name of "Darth" and a second name that reflects his service to the Dark Side: e.g., "Darth Vader" (invader); "Darth Sidious" (insidious); "Darth Maul" (a hammer).
Twi’Lek: Jabba’s palace major domo is one of the mysterious
Twi’Lek.