The Nagas are borne of Lord Brahma, who lay down while doing the work of creation and dropped hair from his body that transformed into snakes. Even while his body crawled along with its hands and feet contracted, there sprang from it ferocious serpents and Nagas with their hoods expanded. The Uragas are also serpentine demigods, who are not exactly demigods but between the demigods and human beings.
"The Nagaloka planet is situated below the earth planet, and it is understood that the sun rays are hampered there. The darkness of the planet is, however, removed by the flashes of the jewels set on the heads of the Nagas (celestial serpents), and it is said that there are beautiful gardens, rivulets, etc., for the enjoyment of the Nagas. It is understood here also that the place is well protected by the inhabitants."
Bhaktivedanta Book Trust. Excerpted from various texts and purports of HDG A.C. Bhaktivedanta Swami Srila Prabhupada.