Dunn civilization developed from nomadic tribes heavily tied to ancestor worship. Once they formed an agrarian society and eventually one based on heavily populated urban centers, the concept of individual ancestors kind of broke off into archetypes. Now, it is most common to worship these archetypes, and certain organizations learn to gain power from them.
The greater Ascended Types are the same as the months: the Mother, the Sower, the Soldier, the Fisher, the Debtor, the Merchant, the Harvester, the Peddler, the Wanderer, and the Builder. There are a ton of lesser types, but generally power is only conveyed by the greater ones.
As far as thinking of it as domains, essentially any domain that you can argue suits the archetype, it is valid. Same thing goes with alignment. Some have developed associations. For instance, the Wanderer is associated with Death (it is considered bad luck to invite strangers into your house during Wendersmonth as it is seen to be inviting death into your home).
Renditions of the Types in art are referred to as “Aspects.” Temples dedicated to multiple types often contain statues and mosaics featuring the Aspects together.
Sometimes, extremely devout individuals are said to have been “Aspected,” in that they gain some measure of power of their chosen Type.