Members are the people who play the game. There are two kinds of members:
Players play the main characters in the story, choosing what the characters do and say, bringing them to life.
Directors plan adventures, set up scenes, and play supporting characters who come and go.
Most games have one director and two to eight players. It's possible to play with larger groups, and even with more than one director, but it's better to start small.
The perfect size for a new group is one director and two or three players.
Characters are the imaginary people who experience the adventures. There are two kinds of characters:
Main characters are played by players. They are the heroes (and sometimes the important villains) of the story. Players and directors work together to set up casts of main characters that are fun for the whole group.
Supporting characters are the people and other creatures that the players encounter on their adventures. Supporting characters come and go. It's the director's responsibility to play all of the supporting characters.
Sessions are occasions when players and directors get together to play the game. Plan for early sessions to take a couple of hours. An experienced group can have a fun session in about an hour, but a good group is more likely to want longer sessions. The longest sessions can last six or more hours.
An adventure is a series of sessions that tell a complete story from beginning to end. A good xg group commonly plays an adventure from beginning to end, then gets together to decide what adventure to start next.