God is not a being with a form, like in abrahamic Christianity, nor does he "create" in the same way the abrahamic god does. Pleroma (heaven) is the result of the Monad's (the true God) contemplation. Meaning, he thought, and his thought forms came to "life in a way"
A troupe of lesser spiritual beings called Aeons were the final step of this contemplation. The final aeon, Sophia created an entity called the Demiurge. Either accidentally or on purpose depending on the sect.
The demiurge then went on to create earth.
In Sethian Gnosticism, the Demiurge is the god of the old testament, and the garden of Eden was actually a prison for blissful ignorance. The fruit merely helped them gain gnosis to see past the demiurge's lies.
In Valentinian gnosticism, the demiurge was actually created as an egregore by Sophia who created earth under the safeguard of the Monad.
In order to reach the Pleroma, one must gain gnosis. Either by rigorous spiritual transfiguration, or by deciphering the parables of the bible. Again, depending on the sect. Your key to gnosis is the divine spark, essence of God still in humanity after the creation of Earth.
Again, depending on the sect, each gnostic will have different views on the type of being Christ was. Some say he was holly supernatural, some say the Spirit of Christ inhabited the body of Jesus, and some still have an orthodox view. Also, views on the relationship between God, the Holy Spirit, and Christ are widly different. Some are trinitarian, some are not. The Holy Spirit has several names. Barbelo, the Invisible Spirit, the Virginal Spirit, are just a few examples.
I think I pretty much got all the main points.