The Vanir (a public domain image)
The Vanir (pronounced "VAH-neer") are a group of very ancient gods and goddesses who originated in Vanaheimr. They are considered the most ancient of the pagan deities in the northern tradition. They are intimately connected with Nature and the elves, and as such are typically considered to be deities of peace, plenty, fertility, wisdom, prophecy and magic.
It is speculated that the word "Vanir" is likely to have derived from a Proto-Indo-European root, wen, which is related to several other words in Indo-European languages meaning "pleasure" or "desire". Numerous other theories have been proposed for the etymology of Vanir, such as that of the scholar Raymond Ian Page who has suggested that while there is no shortage of etymologies for the word, it would be tempting to link the word with the Old Norse vinr, meaning "friend," and the Latin Venus, which is the name for the goddess of love.
Another theory is that the term "Vanir" suggests elemental principles such as force. Under this interpretation, English words such as wan, wane, wander, wand, want, van, vane, vanish, etc., which all share similar sounds, and which all deal with forces and movements, or force carrier principles, may indicate some derivation from the word Vanir; perhaps suggesting that the Vanir were personifications of force carrying principles such as change, movement, fading, bearing, directing, altering, and even longing.
The Vanir (singular Vanr), who are sometimes anglicized as the Wanes (singular Wane), are attested to in the Poetic Edda, Prose Edda and the Heimskringla. All of the aforementioned sources described the deities Freyr, Freyja, and Njörðr (also called Njord) as members of the Vanir, while the Heimskringla lists Njörðr's unnamed sister (speculated to be Njörun or Nerthus), who was also his wife, and the god Kvasir as also being among the Vanir. Also, it has been speculated that Heimdallr may be a member of the Vanir, since he is said to be capable of knowing the future (as is mentioned in the poem Þrymskviða), which is a trait belonging to all of the Vanir, though not necessarily exclusive to them.
The Vanir were said to live in Vanaheimr, the "land of the Vanir", one of the Nine Worlds of Norse cosmology. The precise location of Vanaheimr is unknown, but Hilda Ellis Davidson has suggested that the Vanir are undoubtedly connected with "the land-spirits who dwelt in mounds and hills and water," so it has been suggested that Vanaheimr may have a connection to some sort of underworld. Whatever the case, a definite connection does exist between the Vanir and the land-spirits, as it is known that Freyr was the Lord of the Elves, who ruled over Álfheimr, which was the home of the light-elves, and the elves were most probably a type of nature-spirit.
The exact role and function of the Vanir is unattested, but all the information seems to indicate that they were essentially representatives or personifications of the highest order of powers in Nature, with the elves being more or less their "helpers", who were tasked with much more localized and specific duties.
The Vanir all largely served the same function, and were collectively associated with the sea, the sky and the winds, agriculture, fertility, prosperity, wealth, land, travel, death and birth. They were all capable of shapeshifting and of foreseeing future events, and all of them are associated with seiðr, which was a type of magic or sorcery. Their rites often tended to be sexual in nature, as sexuality was very sacred to the Vanir, and so it should be noted that their code of sexual morality was very different from what most modern societies are familiar with, and such conduct would have likely been considered extremely loose, if not immoral (even among some neopagans), by today's cultural standards.
The chief deities among the Vanir are the brother and sister duo of Freyr and Freyja, whose names mean "Lord" and "Lady", respectively. Freyr is attested to have been the Elf-King in the Prose Edda, and since Freyja is his twin sister and quite probably also his consort (at least prior to the Æsir-Vanir War), it is therefore not unreasonable to assume that his sister Freyja ruled beside him as Elf-Queen. This assumption is supported by Freyja's connection with the Valkyries and the dísir, who were vættir, also known as wights, which like the elves were nature spirits.
A connection between the planet Venus and the Vanir may also exist, especially in light of the relationship between the elves and Venus (see the Elf Cross and also the Ljósálfar), Freyja's corresponding characteristics to that of the Roman goddess Venus, and the twin-sibling relationship between Freyr and Freyja which is characteristic of deities connected with the planet Venus, also known as the Morning Star and the Evening Star (also see Artemis and Apollo).
Some symbols believed to be associated with the Vanir include the: apple tree, ash tree, bees, bells, birds, boars, bodies of water, bread, brooms, burial mounds, cats, cattle, chariots, eggs, fish, fruit, gold, hawthorn tree, honey, horses, leaves, mead or beer, mirrors, the Moon, nuts, oak tree, the pentacle, phallus, pine tree, plows, rabbits, rain, runes (of the Elder Futhark), ships, spiders, spindles, the staff, stag or antlers, the Sun, swords, thread, Venus, wagons, wands, wheat, wheels, and wolves.
The Vanir should be approached with a general regard for respect and gratitude, but at the same time it should be noted that they are not inclined to demand or expect an unnecessary amount of attention or praise, in fact I would recommend that the Vanir be approached much the same way one would approach a friend; that is, assuming that the Vanir do not for some reason decide they would like to initate contact with you first.
Peace and blessings. Alraune.
Sources:
Davidson, Hilda Roderick Ellis (1988). Myths and Symbols in Pagan Europe: Early Scandinavian and Celtic Religions. Manchester University Press.
Faulkes, Anthony (Trans.) (1995). Edda. Everyman.
Grundy, Stephan (1998). "Freyja and Frigg" in Billington, Sandra, and Green, Miranda (1998). The Concept of the Goddess. Routledge.
Hollander, Lee Milton (Trans.) (2007). Heimskringla: History of the Kings of Norway. University of Texas Press.
Larrington, Carolyne (Trans.) (1999). The Poetic Edda. Oxford World's Classics.
Page, Raymond Ian (1990). Norse Myths. University of Texas Press.
Davidson, Hilda Ellis (1993). The Lost Beliefs of Northern Europe Routledge