Short answers, pulled from the story.
The Vanir are one of two groups of gods in Norse mythology, the other being the Æsir. They are associated with fertility, wisdom, and the ability to see the future. Their confirmed members are the god Njörðr and his children Freyr and Freyja.
The Æsir-Vanir War was a conflict between the two groups of Norse gods described in sources including the Poetic Edda poem Völuspá. The Vanir broke through the Æsir's stronghold walls and were described as "indomitable, trampling the plain". The war ended with a hostage exchange and a peace ritual in which both sides spat into a vat, producing the man Kvasir.
Vanaheimr is the Old Norse term for "Home of the Vanir", the realm associated with the Vanir gods. The god Njörðr was said to have been created there by "wise powers", and the jötunn Vafþrúðnir states that at Ragnarök Njörðr "will return to the wise Vanir".
According to Heimskringla, Freyja was the first to teach the Æsir a form of magic called seiðr, as it was practiced among the Vanir. After the Æsir-Vanir War she became priestess at the sacrifices among the Æsir.
In a 2010 publication, Simek argued that vanir was originally a general word for gods and that its use as the name of a distinct divine group was a deliberate invention by the 13th-century author Snorri Sturluson. Simek called the Vanir "a figment of imagination from the 13th to 20th centuries". His argument was rejected by scholars including Clive Tolley, Jens Peter Schjødt, and Terry Gunnell.
Small decorated gold foil pieces called gullgubber, dating from the Migration Period into the early Viking Age, have been found at building sites across Scandinavia, with one site yielding almost 2,500 pieces. Many depict a man and woman with a leafy bough between them. Scholar Hilda Ellis Davidson noted these may be linked to the Vanir, possibly representing a divine marriage parallel to the union of Freyr and Gerðr in the poem Skírnismál.