It is said that they were the spirits of the dead that brought fertility. Of course, with each different culture's myth the story of what they did varied, but most do link them to fertility. They were known to cause disease by shooting arrows at people. Wherever the arrow struck the person was where they would get pain and sickness. They could be appeased with food and drink offerings, if they accepted them they would be kind and helpful to humans.
According to Anglo-Saxon lore there are light - Liosalfar - and dark - Svartalfar - elves.
Oberon is said to be their God. Also, the Norse God Fey is said to be the ruler of the light elves.
Their appear as human type figures with long hair, which makes me think of the Elves from the Lord Of The Rings movies.