Armor Penetration as a stat has been removed since the end of Wrath of the Lich King. It used to reduce the amount of protection a boss had from its armor rating and was useful to all melee classes.
The stat was deemed to complicated by Blizzard, and also was a stat that was so good that everybody was stacking it to its maximum. As such, it has been removed in favor of putting attention on existing stats instead (Haste, Crit, Mastery).
orc gear
wrath
might
Priests due to the fact that they have cloth armor.
Usually with the penetration of a penis stuck into the lady's vagina. Wow! sex
Find an armor vendor and press the repair button in the transaction window.
While Divine Storm, Crusader Strike, and auto-attack benefit from armor penetration, it is not a stat that ret paladins should be stacking tons of on their gear. Most of the paladins attacks are Holy damage. As such, it ignores armor. It has been said on various forums and chat rooms that it is better to get strength with a little bit of intellect mixed in for good measure.
Don't worry about it. Just do dungeons and level up.
Warriors can upgrade from mail to plate armor at level 40.
Anywhere really. Armor drops from monsters, players can sometimes make shoulder armor, or you can often buy (horrible) armor in even small towns. The auction house has some but you'll want to stay away from that till you get a real feeling for the game.
armor is automatically converted when you do a paid faction change.
In the online game, World of Warcraft or WoW, there is one class that can use a spell called hex. That class is a shaman, characterized by their versatility, healer/dps status, and mail armor.