I had named my character Selena because I had made a bet with a friend, and then out of curiosity, I did in console: help Selena and found NPC: Selena 00000007, I know it is not me because my ID is 00000014, This NPC was a girl, and when I spoken to her (I had did player.placeatme) all they said was "Dovahkiin" and did the thing with the hands the greybeards do. I was wondering what quest starts with Selena, or is Selena a testing NPC?

Selena 00000007 is you as the prisoner. She is most likely generated and kept in game via the auto save mechanics. There wouldn't be any quests associated with her. She does not appear in the creation kit nor anywhere on the UESP. When you look up the Form ID 00000007 in the Creation Kit it is for the Editor ID Player for the Prisoner. She may be given a default animation/dialog package as part of being created. Cheers!