Reddit mentions of Gnosis: The Nature and History of Gnosticism

A great go-to book for a scholarly yet clear explanation of gnosticism is Kurt Rudolph's "Gnosis: The Nature and History of Gnosticism".

Also, a little known fact that might interest you is that the Codex Tchacos, the codex that brought us the gnostic Gospel of Judas, was found to also contain fragments referring to Hermes Trismegistus, thought to be from a Coptic translation of Corpus Hermeticum.

You want to start by reading the following book, link at the end. Gnosticism is the search for knowledge, truth. The world that we exist in was made
By the demiurge (God) the demiurge came from the Pistis Sophia which in turn is an existence from the pleroma (the light the first existence etc) that touched the void (it gets messy and my memory is not complete, the book will explain). Now the demiurge creates because It has a sense of the pleroma but cannot be part of it. So in the end man was made and man has been given a divine spark in itself and that spark will eventually go back to the pleroma. The demiurge is evil and gives suffering. There are three types of humans, ones who have the truth inside them which they must share, ones who have the ability to listen to this truth and understand and ones who cannot hear or see this truth at all. It also deals a lot with duality of existence that is a major theme.

http://www.amazon.com/Gnosis-The-Nature-History-Gnosticism/dp/0060670185