Castiel possesses authority and rule over the realm known as Heaven. He only rules over the realm, as for the inhabitants, he serves them: the angels. He guides them and does what he can to help them with their tasks and jobs they're given.
He now serves the angels, but as for his past, well, no one besides him really knows about that. Currently, he works for a Primordial being known as Saintblue. He has free reign over the entire realm and its residents, but Saintblue likes to check in sometimes, making sure his lieutenant hasn't destroyed anything too significant.
Castiel is primarily a generous, kind-hearted deity, even to mortals and other beings. He enjoys his work but wishes he had more angels so he could assist the mortal planes of existence more.
He can only create angels every so often, when he has permission to channel power from Saintblue. However, he can morph souls into angels much easier than creating them from scratch, and this is how a majority of his angels were made.
Castiel works very closely with Satan, the lord of Hell, as well. Sometimes, Satan allows Castiel to enter his realm of the damned to find a poor, tortured soul to save and attempt to redeem. If this happens, then they may become an angel, or they can sometimes go back down to Hell and work for Satan, but that is rare.
Castiel not only accepts questions and opinions or suggestions, but encourages them! He wants as much input as he can get, not just from his angels, but from any other being in existence. He may not use the information but he still welcomes it all the same. He may be contacted at any time, as he also really enjoys getting messages as well.