I'm confused about JJ Abrams initial involvement with the show. Can somebody clarify what his role was?

J.J Abrams was originally a co-creator of what we now know as "Lost" (It was an idea originally from Jeffrey Lieber which was then heavily readapted) along with Damon Lindelof. At the end of the first season as an executive producer, writer and director J.J Abrams decided to ilipat on to other projects, so then Damon Lindelof called on Carlton Cuse to take J.J's place and those two (often called Darlton sa pamamagitan ng fans) now run the show.