Fae or Faerie are separated into two categories: the Seelie and Unseelie.
Seelie Fae are light Fae, while Unseelie are dark. (Note: Light is not always good and Dark is not always evil). The Summer Court is comprised of mostly Seelie and the Winter Courts is mostly Unseelie. The both use Glamour and Iron can kill both.
Seelie Fae are generally the more helpful of the two while Unseelie are known as the tricksters. But the lines are blurred where some Fae are concerned. Take the Brownie for example. This little Fae is a house dweller and is attracted to shiny things. A Brownie will help keep things tidy around your house in exchange for 'payment' (usually tin foil or something shiny). But if you do not give the Brownie payment, you'll find the house in more of a wreck than it started with.
To see Fae they Fae have to give you the 'Sight' or they lower their Glamour. The Sight is the ability to see into the Fae Realm. Its said that the seventh son of the seventh son will be born with the Sight. Their are other ways as well: powder or creams made by the Fae that are applied directly to the eyes.