To sum up - Tarnished are a bunch of dead heroes that were resurrected to try to become the Elden Lord, restore the broken Elden Ring, and revive the Golden Order that ruled the world prior to the Shattering. The Shattering was an apocalyptic civil war between the Demi-gods, children of the great godess Marika. The war started when the Elden Ring shattered and the demi-gods became mortal and able to die. Your character is Tarnished, part of a group of quasi-immortal humans who serve the Two Fingers religious faction and can gain immense power. Most of them are dead heroes from a bygone age resurrected to repair the aforementioned Elden Ring, but your character is an outlier - A nobody, with no power and no great accomplishments, resurrected for unknown reasons.

That’s a basic sum-up of the Lore that is presented to the character in the opening introduction. Not that some narrators may be unreliable.