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As of the latest versions of D&D clerics and holy types like paladins are a little challenging. First off I've noted that earlier core D&D source books like the 2014 DMG had a decent list of pantheons of gods. You'd basically start off as a cleric and right out of the gate you'd be all about some god or other. But the more recent release kind of lets you freestyle where your divine magic comes from, which or how many deities or even misc entities it comes from. There's sort of a blur between Cleric & Warlock, where they're both kind of gaining their powers from other beings, just go about it slightly differently is all. But for a cleric find a list of gods seems to be very important if not at the outset, then at least by level 3.
In my game world I've declared that there are not many (civilized) humanoid gods and have not been for quite awhile. Yet somehow I have Eyrun & Zingle running amuck anyway. So the protocol is that whatever these low level clerics do as the game moves forward, will inspire potential gods to come into being, and that really is what the cleric class becomes - a starting point for creating new pantheons and roleplaying out the struggles to get there.