Armor will Usually give you a bonus in HP, but sometimes it may give you other Bonuses.

Buying and Selling:
Buying Prices are set, some Armor cannot be bought, they either must be found in quests, or Made.
You can Buy an Armor peice when you have the required amount of Golji; to buy one you can either do so Before the Quest starts, during the Quest (if you enter a town), after the Quest is over, or on the Forums (Transfer Records).
You can always sell your armor if you don't want it, the selling price is 1/2 of the Buying Price. You can sell at the same times you can buy.

Stacking: Stacking is the use of wearing multiple armors, you may Stack 2 kinds of armor for the body, 2 kinds for your feet, & 3 for your head. Hands, Arms, & Legs only have 1 catagory level.

Head 1: Glasses/Eyepatches (Must Use only one)
Head 2: Necklaces/Earrings (Must Use only one)
Head 3: Helmets/Hats (Must Use only one)

Arms: Bands
Hands: Gauntlets

Torso 1: Tunics/Dresses (Must Use only one)
Torso 2: Armor/Robes (Must Use only one)

Legs: Pants/Skirts (Must Use only one)
Feet 1: Socks
Feet 2: Boots/Greaves

Underwear: Garments

Armor Lists
Helms Armor Gauntlets Greaves
Helms II Armor II Gauntlets II Greaves II
Headgear Robes Bands Boots / Socks
Headgear II Robes II Bands II Boots II / Socks II