For the Major Advancement: Make a Second Character, how does this work?

For the Major Advancement: Make a Second Character, how does this work?

For the Major Advancement: Make a Second Character, how does this work? Do they have two characters that they rotate in and out at will? If so, how do they earn XP and cred?

Otherwise, do they now have two characters in play at the same time? Or is this more of an MC’s personal interpretation?