Jake is one of the special children picked by the yellow-eyed demon (YED, Azazel) and sent to Cold Oak, South Dakota, in All Hell Breaks Loose: Part 1 to duke it out. Jake's special power is that he is super strong.
Jake and Sam are the last two contenders left at the end of this episode. Sam tries to convince Jake not to listen to the demon, saying they should stick together to make it out alive. Just as Dean and Bobby find them and make their way into the ghost town, Jake stabs Sam in the back, killing him. Jake runs off.
In All Hell Breaks Loose: Part 2, Jake meets up with YED at the edge of the tracks that form the giant devil's trap guarding the gate to hell. We learn that the mission of the last special child left standing is to go in (since YED can't do it himself) and use the Colt to unlock the gate. Coerced by threats and promises about his family, Jake agrees to do it.
Dean, the resurrected Sam, Bobby, and Ellen try to stop him, but Jake manipulates Ellen's gun to point to her own head, making the rest for the team drop their weapons. As he turns away to use the Colt on the gate, Dean and Bobby rescue Ellen, and Sam grabs a gun and guns down Jake.