Characters in a FlexD6 system are pretty simple to create. They have a name, role, and description. In some genres (fantasy and sci-fi for example) characters will also have a species. Characters also have a list of skills, which indicate what the character is good at. The characters role is used to classify the character for narrative as well as helping to determine the character's skills and ability.
There is no class system in this game. It is all driven by the skills and special abilities you pick for your character, allowing you to create very unique characters.
The Role is used more for narrative and guidance. Facilitators may use the Role when determining advantage and disadvantage. Applicable roles depend on the setting. For example, in a fantasy setting, some common roles would be Cleric, Magic User, Fighter, or Rogue. In a space setting some roles would be Pilot, Smuggler, Bounty Hunter, or Engineer.
In some genres characters will be of a certain species. In a fantasy setting, that could be an Elf, Dwarf, Halfling, Human, Lizardman, etc. Many species have unique abilities like seeing in the dark, being a natural with a bow, or being very crafty. These abilities should be unique to the species and very likely will not be available to any other characters unless they share the same species.