The user identifies a target, and it created a vortex in space-time once the target lock has been established. It allows the target to travel in the past (or future, if the target isn't 16 years old yet) to meet their sixteen-year-old selves. Of course, it came with the limitation that it wouldn't work a target whose lifespan was shorter than 16 standard years.
Rakata tested his prototype on two Institut de Marquain athletic legends: Catherine Mouranger, which was a high school contemporary of the designer, and Dunames Lopez, right around the time where they earned their respective spots in the school's athletic history. Due to the danger such devices caused, Janielle Potvin, acting under Department of Temporal Investigations protocol, seized the device. (Star Trek: False Vacuum: "Dear Sixteen-Year-Old Me")