Green Lantern is about an organisation of space cops who use alien technology in the form of rings which allows the user to make physical constructs out of Green energy based on their will. In the last few years there has been a huge ongoing storyline showing that there are seven types of energies based on different facets of human character. The green energy is based on willpower. Yellow is based on Fear. This collection deals with Orange, based on avarice.
To understand the short collection of stories in this book you first need to read Green Lantern Rebirth, then SInestro Wars. It also probably helps to read Rage of the Red Lanterns and Sins of the Star Sapphire. Basically, all seven energy types are now being used, leading to a growing galactic confrontation. This is all building up to the Blackest Night story. Agent Orange deals with the Green Lanterns discovering who is using the Orange energy, and that it is linked to yet another secret from the dark past of the Guardians, who as ever come across as self involved, arrogant beings. Its a decent story, but it is very much an intermediate one, so won't be of any value unless you are collecting the entirety of this giant story arc.