Not much to them, at the moment. None of the primordial ones have been fleshed out, they mostly just exist in order to explain things like gravity and time.
The 2nd generation or "baseline" gods are like those found in real world mythology. They shaped the world and have clashing personalities. The origin for humanity is that the god of wisdom saw how the other gods were constantly fucking up the world with their bickering, and convinced all the gods to work together to create something that belonged equally to all of them, resulting in humans. Eventually the gods started fighting again, splitting up into factions that attempted to recreate and improve upon humanity (creating the other races in the process). At least now they pull their punches, so as not to put too many humans in danger (as each god sees humanity-as-a-whole as one of their children).
The ascended mortals are all former humans, as they have a hint of each god within them. The first one to ascend was The Torchbearer. They no longer have a physical form, instead appearing to people in prophet, symbolic visions, literally and metaphorically lighting the way "forward" for that person. There's also The Rot King, who (while human) pissed someone off to the point that they bashed his head in and buried him alive, resulting in a sort of super-ascension, where he has multiple domains (madness, buried secrets, undeath)>>79746714
It's a mismash of:
T.E.S. Lore (Daedra, The Make Way God, and Sithis in particular)
Green Lantern (The Emotion Entities)