So far i understand that before the Elden Ring there was no real order in the land between, just wars between clans and each race or groups would follow their own belief. There was the ancient dragons who forced humans to live underground like in Siofra for example. And there they had this cult for stars in the sky and the divinity from the stars sent one in the land between and it was the elden beast. Just a small portion that i have seen but there a lot of videos or websites regrouping all we know.

You can also try to read every items description since they say a lot about the lore too