HBO's Watchmen is already big, thanks to a decades-old fanbase and a mystery-shrouded production anxiously watched over by said fanbase. Famously salty creator/probable wizard Alan Moore is pointedly not involved with this version, or any filmed version of the comic book he wrote, after stating many years ago that the Watchmen series published in 1986 and 1987 ought only to exist in its paper-and-ink form, and that putting it to film would ruin it -- which, uhh, pretty much happened exactly the way he said it would with Zack Snyder's adaptation in 2009.
But Damon Lindelof's Watchmen is different. It's not a panel-for-panel remake of the comic, for one thing -- it barely has anything to do with Dr. Manhattan, Silk Spectre, and the Comedian at all, although the comic book characters do exist in the world of the show. Because the events of the Watchmen comic are baked into the Watchmen series, you could watch it without having read the source material.
But there's some stuff that does come up in the premiere and subsequent episodes -- like name reveals, Easter eggs, allusions, etc. -- that may hang you out to dry if you don't have a teensy bit of background on the subject. I'll be addressing the various things you need to know in this article and updating it after each episode as the season goes on.