I found some info on WIKI:
At the end of Terminator 2: Judgment Day, Sarah, John and the Terminator successfully destroy the T-1000 and the arm and computer chip from the first Terminator. Sarah and John then watch as the Terminator is lowered into a molten steel pit in an attempt to destroy all future technology that could be used to create Skynet. Sarah and John now find themselves alone in a very dangerous and complicated world. Fugitives from the law, they are confronted with the reality that still more enemies -- from the future and the present -- could attack at any moment.
Prompted by the return of the Terminators into their lives, Sarah and John decide to stop running and focus on stopping the birth of Skynet. They are aided by Cameron, a Terminator who poses as a student at John's school and whose mission is to protect John. Meanwhile, an FBI agent named James Ellison pursues Sarah and John with the belief that Sarah is deranged.
An advanced script review by TV Squad revealed that time travel will play a major role in the series premiere including a temporal leap for the main characters from 1998 to the current year. This was also confirmed by the trailer posted on the Fox Fall Preview page for the show.Three video clips from the upcoming series premiere published on the IGN website included the evil Terminator using Sarah's voice over the phone to find John, Sarah and John fighting over their current situation, and the evil Terminator looking for John, Sarah, and Cameron at the Dyson residence.