Here is a good guide
I was gonna go full on Bear tank but relized it's not that fun, so I started que'ing heroics and running as feral kitty. I like feral kitty alot more, so my question is... What should I be gemming? Do I stick with gem socket colors or ignore them? I see some running all Armor Pen, is that viable now?
-So I just stand in the corner and take all the damage?
-Correct, your the tank.
-I'm going to go re-roll
As a newbie Cat I would stick with Agi gems to start out with. Eventually you will want to make the switch to ArP but only after you've acquired large amounts of it on your gear and possibly a trinket like the Needle Encrusted Scorpion. At lower gear levels the extra agi might help with the rotation by providing more combo point generation through increased crits. Rawr is a nice tool to help with gearing and gemming choices.