What is Gnosticism?!?

I'm Doug A level philosophy and were studying the religious and scientific beliefs on the creation of the world, i think i know what Gnostics believe regarding this but I'm not sure...
do they believe that God created the world out of Prue existing matter, and that matter contained evil and that's how evil got into the world? God just shaped the evil Prue existing matter into what is our world?

any help will be much appreciated!!

Gnosticism is a belief which advocates that the world was created by an imperfect God. The existence of further divisions from this larger divine entity that is believed to be imperfect and away from the true one source of all divinity.

Gnosticism

Religious and philosophical movement popular in the Roman world in the 2ND?3rd century AD.

The term, based on the Greek nosies ("secret knowledge"), was coined in the 17Th century, when it was applied liberally to ancient Christian heretical sects, especially those described by their orthodox contemporaries as radically dualistic and world-denying, and those who sought salvation through esoteric revelation and mystical spirituality. In the late 19Th and the early 20Th century, that view of Gnosticism was replaced with several groupings, and the discovery of the Nag Hammadi texts in 1945 greatly enhanced the understanding of Gnosticism. The relationship with ancient Christianity remains uncertain, but the Gospel of Thomas and the Gospel of Mary (which portrays Mary Magdalene as a leading apostle) are generally seen as being grounded in Gnosticism. They emphasized the teachings of Jesus, rather than his death and resurrection, as the key to salvation. The teachings of Valentinus were the basis of the Gospel of Truth, a fusion of Christian and Gnostic beliefs. Other texts previously considered Gnostic are now assigned to distinct religious traditions, especially Hermeticism (see Hermetic writings), Mandaeanism, and Manichaeism. The texts of the Sethians have the best claim to the designation "Gnostic"; they describe one supreme, good God and the creation, by a junior heavenly being (Sophia), of an arrogant creature who then claims to be God. That creature withholds from humanity moral knowledge and eternal life, but Sophia plants the divine spirit within people to save them. Male and female saviours (including Jesus) were sent from the world above to instruct humanity in the knowledge of the true God and humanity's own divine nature. In general, Gnostics taught cosmological dualism, strict asceticism, repudiation of material creation as evil, docetism, and the existence of the divine spark in humans.

According to the source below ancient Gnostic's believed that since matter was evil and God the spirit was all- good, there was an intermediary between God and creation:

"The Christian Gnostic teaching is traced by historians to Simon Magus a magician in Samaria. He is said to have written the Gnostic work entitled The Great Revelation in which Simon is the Messiah, not Jesus. Menander was one of Simon's disciples. He preached that those who followed him would not die, and that instead of Jesus being crucified it was Simon Magus. Their philosophical system had a structure of emanations that began with God the supreme self existing Spirit who through epochs of time emanated from Him other beings, called AEons (Gr.Palermo-fulness). Through them He limited His own infinite being manifesting in each, one of His divine attributes. Since matter was evil God could not have created the world directly. The gap between the spiritual world and the physical world was bridged by a series of emanations. Then this divine Spirit called AEon united himself to the material body of Jesus. Christ was descended from the heavenly stratosphere and united himself with a person whose body was formed out of psychic substance. So He was not truly God nor human. Cerinthus in the late 100?s taught the Gnostic teaching of the existence of AEons and emanations from the eternal God. Also that Jesus was the natural Son of Joseph and Mary and the Christ came upon Him at His baptism and left him at the crucifixion (like the Ebionites and the New Age teaches today), so only a man was crucified."

"Salvation to the Gnostics came by knowledge and experience. Those who did not have this knowledge (esoteric truth) were associated with ignorance. They received direct revelation from the Spirit which was more important than the word."