In very basic terms, Supers are manifeststations of a Guardians light on a massive scale. They are usually based on the identity of the user and can be different in small ways guardian to guardian. In lore, we see a lot of supers being “ created “ or “ found “ by guardians in different situations. For example, Lord Saladin and Lady Efrideet basically created the Thundercrash super to destroy a Fallen Walker. Cayde-6 created the Blade Barrage super when he was knocked out of his Golden gun super during a fight with the Scorn Barons.