Every person in the SCA picks a name to go by in the Society. It could be something simple and familiar (Mary of London or Thomas the Smith) or something elaborate (Oisin Dubh mac Lochlainn). With that said, no one may use the name of an actual person from history or legend (such as Richard the Lionheart).
The SCA has its own College of Arms to help you select and register an SCA name and heraldic device. The College of Arms has many resources to assist members in their research, to ensure that their names and devices are appropriate to the world we try to recreate and that each registered name and device will be unique.
Don’t worry about figuring out a name before you come to events. Many people go by <real first name> of <name of SCA group> for a while until they figure out what name they’d like to adopt.
Some SCA members try to create an entire “persona” for themselves, as someone who could have lived in a specific time and place within the scope of the SCA, fitting their costume and activities to that persona. Some dedicated people try to behave at events as if they actually were their persona. Others simply pick a name and go ahead with life in the “Current Middle Ages.”
Even our local groups have their own names. Lansing, Michigan is “The Barony of Northwoods”; Toronto, Ontario is “The Royal City of Eoforwic”; Boston, Massachusetts is “The Barony of Carolingia”; and the San Francisco Bay area is the “The Principality of the Mists”.