The Green Lantern TV Series by CW is a spinoff of Arrow and The Flash, and reboots the Green Lantern Saga. It will act as GL's reboot in the DC Cinematic Universe, and will tie in to Justice League in May 2017, right after the Season 2 Finale.
This happens a few months before the events of Man of Steel
Hal Jordan (Jensen Ackles) makes his first appearence on the CW on The Flash Season 1 finale, where Barry Allen/The Flash meets Hal Jordan to investigate an Alien Crash site at Ferris Aircraft in Coast City. During this time, Hal Jordan is given his Power RIng by Abin Sur, the Alien in the crash site. The last shot of the Season Finale shows Hal Jordan leaving Earth in a ball of green energy.
Season 1 Plot/Antagonists:
This happens right after the events of Man of Steel. The primary plot of Season one, episode one is Hal Jordan learning the ways of the Green Lantern Corps. The second episode shows Hal Jordan attending Abin Sur's funeral, meeting there main antagonist Amon Sur, before being attacked by Manhunters, the killers of Abin Sur. Throughout the season, Hal visits several planets (Biot, Oa, Zamaron, and Earth), fighting many manhunters and Zamarons, and it is revealed that Amon hired the manhunters to kill Abin Sur in exchange for giving them access to Yellow Power Rings, and himself access to his father's power ring. This backfired when Hal received Abin Sur's ring, not Amon. Amon is beaten by Hal and Kilowog, and his Yellow Power ring is destroyed, and Amon is imprisoned.
Season 2 Plot/Antagonists:
The main antagonist of Season 2 is Thaal Sinestro, founding the Sinestro Corps after using his own yellow power ring, out of jealousy and envy of Hal beating Amon, not himself. Hal and Sinestro battle it out most of the season, before Sinestro mysteriously disappears. Sinestro returns in the Sequel to Justice League as a member of the Legion of Doom, under the command of Vandal Savage.
Jensen Ackles as Hal Jordan/Green Lantern
Grey DeLise as the voice of Green Lantern's ring
Christina Wren as Carol "Carrie" Ferris
Marton Csokas as the voice (and motion capturing) Thaal Sinestro
Kevin Michael Richardson as the voice of Kilowog
Kevin Durand as the voice of Amon Sur