Short answers, pulled from the story.
Njörðr is a Norse god belonging to the Vanir, a faction distinct from the Æsir. He is associated with the sea, seafaring, wind, fishing, wealth, and crop fertility, and lives in a hall called Nóatún. He is the father of the deities Freyr and Freyja.
Njörðr married the mountain goddess Skaði, daughter of the giant Þjazi, after she came to the Æsir seeking compensation for her father's death. Their marriage failed because Njörðr wanted to live near the sea while Skaði wanted to live in the mountain home Þrymheimr. Neither could tolerate the other's landscape, and Skaði eventually returned to the mountains permanently.
Njörðr was sent as a hostage to the Æsir at the end of the Æsir-Vanir War as part of a peace agreement. The Vanir sent their most outstanding men, Njörðr and his son Freyr, in exchange for the Æsir's Hœnir. Odin later appointed Njörðr and Freyr as priests of sacrificial offerings.
Both Njörðr and Nerthus descend from the same Proto-Germanic theonym *Nerþuz. Nerthus, described by the Roman historian Tacitus in his 1st century CE work Germania, is the feminine Latinized form of what Njörðr's name would have sounded like around 1 CE. Scholars debate whether the gender difference reflects a grammatical shift in the Germanic languages or the evolution of separate religious traditions.
Njörðr appears in Heimskringla, Snorri Sturluson's collection of Kings' sagas, where he is presented as an early human king of Sweden whose reign was marked by peace and good harvests. He is also invoked in a 14th century Hauksbók ring oath, and his name appears in numerous Scandinavian place names in Sweden, Iceland, and Norway.
Veneration of Njörðr survived into 18th or 19th century Norwegian folk practice. A tale collected by Halldar O. Opedal records a woman named Gunnhild Reinsnos, born in 1746, thanking the god Njor by name after a successful night of fishing on the Sjosavatn in Odda Municipality, Hordaland.