Final answer:
Jim Halpert started his first day at Dunder Mifflin Scranton in the pilot episode of The Office.
Step-by-step explanation:
In S1E1 "Pilot", Jim Halpert started his first day at Dunder Mifflin Scranton.
"Pilot" is the first episode of the television series The Office. In this episode, Jim Halpert, played by John Krasinski, starts his first day at the Scranton branch of Dunder Mifflin, an office supply company where the show is set. Jim's character plays a significant role throughout the series, and his first day at Dunder Mifflin sets the stage for many of the dynamics and relationships that develop over the course of the show.