Thank you, I hope you enjoy the game!
To answer your question: you can roll during the memory scenes if you want to—sometimes a little RNG helps you work out the story. But their primary purpose is to flesh out the characters’ backstories, their relationships to one another, and the setting in general. To that end, I usually run them as the main character or characters the memory revolves around get the most narrative control, and as the GM I just ask lots of questions.