For some it is a belief in different deities, for some it is simply the rituals, for some it is just a pathway where the rules make more sense and it isn't necessary to believe in gods at all. For some it makes sense to celebrate the rebirth of the new year at winter solstice, and the equinoxes in the same way non Christians celebrate christmas and Easter (Even the name Easter is pagan in origin Eostre). They say and it is probably close to the truth that there are as many types of paganism as there are pagans,even Wicca has nearly as many faces as there are Wiccans.
I see it as a structure for a spiritual pathway, I dont worship gods or goddesses as I don't believe in them, but I do feel that it helps me connect to the Earth and its rhythms, to live more kindly, and minimise my impact on the planet. We are creatures not solid but of energy, it seems possible to me that it is at that level we are connected with the universe