Any spec can tank fine up until the Outlands. Then you'll even be fine up to Underbog. Around that time people will start asking what spec you are if they need you for tanking.
Check the sticky on the Warrior page. There are builds in there.
As for the rotation on aggro.
-Single mob= Saunder, saunder, saunder, saunder, saunder, saunder. After your 5 saunders do what you want. If you want to throw in a T. Clap between short saunder cool downs go for it. Demo. shout in between, sure. You want to throw in a Shield block to get a Revenge almost every time, sure. If your Revenge comes up press it.
-Multi-mob= Mark the DPS mob. Saunder the heck out of it. Thunder Clap for multi mob aggro. Thunder clap everytime the CD is up. Keep saundering/revenging the main dps mob. Simple. If you see a stray go towards a caster, and you don't have a off tank either: 1)they run to you, then you taunt; or 2) you run to them and taunt.
Meh, read the stickies it'll go into a bit more detail. There's a good T.Clap Vs Beserker stance/ Whirlwind discussion.