Ringing metal and slamming shields
I'm assuming that if you've chosen to level as a warrior, you've done so because the raw physicality and no-frills approach of the class appeals to you. If that's the case, then protection is definitely that. Protection warriors effectively tank by strapping as much metal to themselves as they can walk around in (mail until level 40, plate thereafter) and daring things to hit them. The rage mechanic means that protection warriors gain more resources to hit back the more they get hit. Protection is also one of the most mobile tanking specs, with multiple ways to move around the battlefield.
It is this mobility that also makes protection so much fun for PVP (player vs. player) combat, as well. Prot warriors might not be the most dangerous killers out there, but they can be significantly hard to stop and have a lot of tricks to exert battlefield control. When a class can AOE stun, disarm, interrupt spellcasting, silence, and stun individuals while themselves moving from place to place, it has great potential for disrupting other people's attempts to kill it or heal others. The prot warrior may be the best possible choice to lock down an enemy healer in a battleground.
A spec to start off with
This is a prot spec aimed at serving as both a leveling spec for instances and one for soloing while leveling. It's not at all aimed for raid sustainability, but rather for allowing you to kill several mobs while taking as little damage or healing as possible (hence the two Victory Rush glyphs and Impending Victory, to give you a prot execute). In this spec, you will be hitting Shield Block on cooldown to increase the damage of your Shield Slams, hitting Heroic Strike to try and proc Incite, and hoping for parries to let you boost that Incite crit rate even higher for more Deep Wounds damage.
This is a spec aimed at putting damage on multiple mobs while focusing one down, getting Impending Victory to light up Victory Rush to heal you, and then once the first enemy is dead, using Victory Rusk to pop you back up to full and starting on the next, already weakened target. The goal here is to grind down six, seven, eight or more mobs. By the end, you'll still be at full health, your Vengeance will have stacked up, and they'll all be dead.
This is the power of the leveling protection spec, especially once you're far enough into the class to be close to level 43 (the first level you can get Impending Victory). Prot's ability to not only take a beating but to regain health while doing it while under attack from many enemies and use those attacks to gain attack power via Vengeance is a very strong leveling tool.
For the first 30 or so levels after you choose you spec (so from 10 to 40), the only real stats you need to worry about are strength and stamina. As you level, you'll mix defensive stats (dodge, parry, and mastery for block rating) with offensive stats (hit, expertise, and mastery for rage generation via Shield Specialization). By the time you're 85, you'll probably build a threat set and a survival set, but for leveling, you should just keep strength, stamina, mastery, and dodge in mind. These stats will serve you well enough as you grow.
Three ways to grow
There are three basic ways to level, and protection probably has it easiest of the three warrior specs in that it can take part in all of them. The spec I linked above is an effective way to solo, do quests, and grind mobs. In addition, it will work fine for instance tanking. Assuming that this is not only your first warrior but your first character, running instances is absolutely the easiest way to get gear stronger than the green drops you can find on mobs and occasionally find on the auction house. Finally, you can run various player-vs.-player battlegrounds (BGs, for short) and pit yourself against other players. All of these grant experience, and BGs also grant honor points, which can be used to buy equipment or saved to trade in for justice points to buy gear once you're at max level.
The basic rotation and how not to be seen dying
Prot warriors don't have a lot of fancy tricks. As soon as you get one of the two shouts that grants you rage (Battle Shout at level 20 or Commanding Shout at level 68), you'll want to use one of them to make yourself stronger and generate rage. You'll most often Charge into combat (especially once you get the talent Warbringer) and use Shield Slam as your first big attack, with Thunder Clap, Devastate, Revenge, and Shockwave all coming into play as you gain access to them.
Heroic Strike or Cleave will become what are called rage dump abilities. You'll use HS when you have one target you want to put damage on and Cleave for multi-target groups. Your soloing rotation won't be any different than your tanking rotation. The goal is to use Shield Slam and Revenge as often as possible, Devastate to keep your Sunder Armor debuff up, and the Rend/Thunder Clap combination when dealing with many mobs you wish to try and keep focused on you. Shockwave has a relatively long cooldown, but in pulls of more than two, it's also worth using as often as you can.
When you're in risk of dying, you can use Shield Wall, Enraged Regeneration, Shield Block (you should be using it anyway to increase your Shield Slam damage), and Rallying Cry. You can also spec for Last Stand. These abilities are designed to keep you alive in one way or another. Don't be afraid to use these abilities while tanking. A lot of starting warriors hoard these, not wanting to use them and then not have them for later. Letting yourself die now because you're afraid you'll die later doesn't help anyone. These abilities are all fairly short cooldowns, between 2 to 5 minutes (even less for Shield Block) and are meant to be used. Used properly while soloing, they make a protection warrior almost invulnerable.
A properly timed combination of Shield Block, Shield Wall, Rallying Cry, and Enraged Regeneration can reduce incoming damage significantly while healing a warrior almost to full. Combined with Impending Victory and Victory Rush, protection warriors become juggernauts who refuse to die when compared with other warrior specs.
This is more than enough information to start with. I've written fairly exhaustively on protection in Cataclysm; you can find my posts as follows to give you more to chew on as you move forward from a beginner's standpoint.
Next week, we're most likely going to get a bit conceptual. It's been almost 9 months since Cataclysm
launched, and we're still seeing queues in heroics. Is the answer to look back to Wrath
At the center of the fury of battle stand the warriors: protection, arms and fury. Check out more strategies and tips especially for warriors, including Cataclysm 101 for DPS warriors, a guide to new reputation gear for warriors, and a look back at six years of warrior trends.