Gnostics were a diverse group of sects scattered across the ancient world with a wide range of interpretations of the gnostic experience. The later being the direct experience of divine reality and the apparent revelation that ordinary reality was an illusion.
The Gnostics were highly eclectic in their choice of material for their mystical systems and interpretations, this was partly a deliberate attempt to free themselves from tradition.
They shared many key beliefs with earlier Orphism and the first Gnostics may have derived from a heretical strain within the Orphic Mysteries. But they also had many differences.
Common features of Gnostic sects include the rejection of an evil authoritarian Demiurge (and his servants the Archons, derived from pagan gods in a role similar to the Orphic Titans) in favour of a more anarchic Supreme Being (though some reversed this), the affirmation of the Goddess over male centred divinities,
personal interpretation of religious experience, a strange mix of ascetism and decadence and a taste for Magick.