You can be pretty sure that Pet aggro is 100% based on growl.
Especially on the lower levels. Growl is always on when you start a hunter, and most dont even know about it.
Tanking with the Warrior kind of feels like playing the Organs.
Thunder Clap is your obvious AoE tank tool till you get the shockwave. And when you have the shockwave, you should use both.
Always try to get your group of mobs together before you thunder clap the first time. If one mob comes later, click on tab and heroic strike it or something.
It also makes your enemies Hit slower, which makes you survive longer/drains Healer mana less.
I usually save the Shockwave for situations where I need Snap aggro and Thunder clap is on Cooldown, but thats just me.
Heroic Strike is your Rage-Dump. If you have too much rage, or your other skills are on cool down, hit the Heroic Strike to do some dmg/aggro.
Im using the Heroic Strike glyph with my Tank warrior, that combined with the 2nd Tier Tanking talent that gives you 15% crit for heroic strike is just cool.
Shield Block is a nice tool against big groups of enemies, but I generally have it on cooldown, even against single mobs.
Shield block makes your block go to 100%, which means that every hit you get in will get converted into Rage (Shield Specialization Talent).
Blocking also means a chance for Revenge to Proc, and Revenge means that your Shield Slam Cooldown gets refreshed.
Shield Slam is the #1 Awesome Threat skill. Use it always on CD.
Cleave is your choice for multiple mob groups. Glyph helps I guess. Dont forget that Cleave and Heroic Strike share their Spot for "on next swing" skill.
Sunder Armor/Devastate: the old #1 Threat skill, now still very cool. On bosses get it up to 5 stacks and keep it up, your DDs will thank you for that.
Otherwise a cool skill with no Cooldown to slap onto fresh mobs and enemies when your have everything on cooldown.
Revenge is that one skill that procs when you dodge/block/parry an attack. Keep it on your bar or bind it to other skills, its a very strong skill and needed for sword & board (which you unlock later, but anyways).
Demo Shout is kind of cool to use when you have nothing to do, but its actually better left for the Fury Warriors to do.
The other stuff is all pretty much situational and optional , like Shield wall as an example, or spell reflect, but I think they are self explaining.
All in all you have to learn how mobs behave. Especially Casters. You might want to pull stuff around the corner sometimes so that the casters follow, and when you tank groups, you should click tab often, to build aggro on as many targets as possible, as sometimes Thunderclap isnt enough (it is on low levels though).
You might want to get a gun/bow/throwing weapon for those tricky pulls, or Pull with taunt (dont Pull with taunt in endgame content). Play around a bit, and learn that stuff. Its not realy all that hard.
As tatile said, Tankspot is the #1 site for Tank informations (the DPS info is cool too)
Elitistjerks is also good, but they're better for DPS in my opinion.
You could of course use both sources to get your infos.
[EDIT] GREAT WALL OF FUMAAAN
.
. So yeah, I think I might be okay when I tank, having played the other side. 
(money was also a factor to me stopping). I was in nagrand, US west server.