What advantages do the different armor types provide?

Armor in the Elder Scrolls series falls into two main categories, Light and Heavy. Within each category, you have a series of grades of quality, which are generally materials (Glass, Steel, Leather), but occasionally based on a style of construction or ore used (Dwarven, Orcish, Elven, etc.)

Orcish is a superior grade of armor to Dwarven - it offers superior protection, piece for piece, than Dwarven does.

It seems to work similar to how it did in Elder Srolls IV, just with more grades.

Lists are ordered from less armor protection to greater armor protection:

• Light armor: Hide, Studded, Leather, Scales, Elven, Glass, Dragonscale
• Heavy armor: Iron, Steel, Dwarven, Orcish, Ebony, Dragonplate, Daedric

Keep in mind that you might find a fine iron helmet that offers more armor points than some of the lower steel ones, but it will weigh more and be worth less gold, and so on.

Also there are other considerations than just armor points, including how quiet the armor is, how cool it looks, and all that, but this list makes a good rule of thumb.