Talk to Katy, Vault 81's teacher and she'll ask you to talk about the Commonwealth in front of her class. Agree to activate the sidequest. Next, you have to talk to her again when she's in the classroom with her students. You can sit in the classroom if you want and wait for a few hours until the classes start. Just select whatever story you want to tell the kids. After the story, you'll get a free Grognak the Barbarian comic.