I'm in the process of planning a timeline of events for the Demonic Paradise but to help you out I'll try and give you the basics.
It follows the basic story of Genesis and elements of other creation myths. God and His wife Asherah help create the universe, They fight Azathoth and the Ogdru Jahad before imprisoning them with the archangels. The Primordials are created to stabilize the aspects of the universe whilst the archangels hunt down and destroy the Ogdru Hem who were creations of the Ogdru Jahad and dealing with other unwelcoming anomalies like the Upside-Down Man. Knowing that the Earth could be in danger if the Ogdru Hem find it, Asherah has the Primordials produce the second generation of deities like the Titans and what not who go to Earth and protect it from the Ogdru Hem. They start to think that hey since we're doing a better job than the Big Man Upstairs and his pigeon kids, we should be the rulers of the Earth and its inhabitants. They soon have kids on their own who turn on them and take rulership over the Earth, only to deal with the problem their parents were supposed to deal with; the Ogdru Hem. The Old Gods fight and win against the Ogdru Hem, and while their resting after they imprison the Evils that spawned from their war inside Pandora's Box, it gives the opportunity of alien races, i.e. the Elder Things, to play around with Earth's life forms which leads to the creation of the Primal Apes.
What follows is trouble in Paradise. God creates humanity, Satan and several angels don't like that. Lucifer doesn't want to be under his Father's control and a war breaks out in Heaven but they lose. The war also damaged one of the Sentinels of Creatio, that being the Scarlet King, who goes on a rampage and wants to destroy the Tree of Life because the war opened his eyes to the tumultuous noises of light and creation. The Scarlet King kills most of his siblings, the archangel Michael and the six other archangels defeat and imprison him, but his tampering with the Tree of Life's roots created a big misalignment and this results in physics and time/space going haywire leading to the Convergence.
The pagan gods also create their own humans, and they live alongside Adam and Eve on Lemuria. Then there's the Fall of Man, Cain kills Abel with Satan's influence. Sin and Evil corrupts the land outside of Hyperborea which is the Golden Kingdom of Man as it is protected by the Secret Fire of God that they managed to keep if only a small amount thanks in part to the angel Anum. Things go wrong, Hyperborea sinks to the ground, and they split apart, regressing into primitive savages. Prometheus pities them and he gives them fire that was kept by Zeus so he could control humanity better.
God wants to make sure that humanity is kept in check after Prometheus gave them back the knowledge of fire so He assigns the Watchers to observe them closely. But again, things go wrong, when Naamah one of Eve's sisters and Adam's former wives, seduces the Watchers into mating with human women and with the corrupt knowledge given by some of the Watchers and the tyranny of the Nephilim, the Earth is engulfed in Evil and Sin. God sends a Flood to wipe out all the Evil and Sin of the world except Noah and his family. When the Flood waters recede, humanity starts anew. Humanity is united again under the rule of Nimrod, the first ruler of mankind after the Flood Age and is trying to bring back the Golden Kingdom of Hyperborea but under less pleasant circumstances like the Tower of Babel. When the Tower of Babel is destroyed, the united humanity spreads out throughout the Earth, and they start to make their own languages and cities like the Mesopotamian Empire, the Ancient Egyptian Empire, Mycenaean Greece and so forth.
That's basically how everything starts in-universe and where the rest of the events pick off like the Werebeasts, the Deathless War, the Gigantomachy, Sparda's rebellion, and so on. If you have any more questions on the timeline of events feel free to ask.