what are the basic things you need to know about ballet?

The title "ballerina" is given to the one top female ballet dancer in a professional ballet company. So, not all professional ballet dancers are ballerinas. Most aren't. Dancers training for a ballet career dorm at ballet academies where they take 20-30 hours of ballet classes a week year round and are either home schooled or get their academics as arranged by their ballet academy. Training is complete by age 16 when a dancer would apprentice with a professional ballet company. In order to get into a top ballet academy, you are screened for body, facility and musicality or they wont train you. Only 2% of the population has what is required. Dancers in ballet companies have ranks starting as corps de ballet, then soloist, and top tier would be a principal dancer. Although principal dancers have most of the leads in the ballet productions, it does not exclude anyone from within the company getting a lead part if they are cast in it. For example a new corp de ballet member of New York City Ballet was cast as Juliet in a new production of Romeo and Juliet several years ago.
If you wish to read more about what ballet training and being in a professional ballet company read Bunhead by Sophie Flack, former NYCB corps de ballet member.

* Standard ballet classes are 90 minutes in length. They start at the barre for about 45 minutes and then move to center and then across the floor for the remainder of the class. Dancers go "en pointe" (start with pointe shoes) at age 13 after many years of ballet training in flat shoes. In class, student dancers wear leotards and tights and their hair in a ballet bun. No jewelry or nail polish is allowed in class. Professionally training dancers are not allowed to wear additional ballet clothing such as leg warmers unless they are injured or between classes to keep their muscles warm. Wrap skirts are worn in variations classes or ps de deux (partnering) classes only .

forget it.