Frequently Asked Questions:
A: Item Meta-stats has a summary as you mouseover/click the item name.
There are also some general rules:
A: First damage reduction from AC is applied as described in Help. Next, damage may be further reduced by Endurance; Endurance does not translate into AC per se. Endurance applies to both magical and physical damage.
A: Tattoos are armor that gain levels the more you fight with them equipped. See Item meta-stats for details on what powers the different tattoos have.
Tattoos take up both a body armor and a cloak slot, and cannot be equipped on the same minion as a Power Shield. Only one tattoo may be equipped per character.
A: Tattoos gain experience when your minions do, in battle. This experience is automatically "trained" at regular intervals; if you're impatient, going to the Train page yourself or unequipping the tattoo will force converting any untrained xp immediately, but there's no reason to do this past the first few levels.
A: No. Neither does the number of minions you have affect how much your tattoo gains.