Amulets are an armor item able to be crafted in 3 different tiers and are equipped in the Amulet slot. they seem to provide no obvious bonus, and no armor rating.
Amulets function like potions. You can place an amulet into a brewing stand and "brew" potion effects into them. Once they have an effect, wearing the amulet gives you the effect while you have it equipped. For example, brewing a potion of regeneration into a gold amulet will give you a slightly weaker regeneration effect than a normal potion, but the effect will last until you remove the amulet or until it breaks.