Searing Totem has a few drawbacks to keep in mind: like almost all totems it has low health and can easily be killed by a target it aggros if you don't have aggro on it yet. Also, searing totem randomly targets hostile mobs within 20 yards of it, meaning that it can aggro a nearby mob if it wanders into range and gets hit, it can break CC, and there's no guarantee that the totem will attack the mob you're focusing on if you have more than one to deal with. Still, for a beginning totem it's pretty effective and generally useful, even cheap for the mana cost over the duration of the totem's existence. A lot of guilds use Searing Totem to good effect during the Leotheras the Blind fight in Serpentshrine Cavern - placing the totem where Leotheras is intended to be tanked in his blood elf form helps ensure that he'll run back after his whirlwind phase as the totem is likely to hit him as he comes out, often causing him to run back to the tanking spot to kill it.
Fire Nova Totem is the first effective 'area' attack a shaman gains at level 12. However, there's a few significant downsides to using it, one of which is the long time between dropping the totem and it actually delivering its fire area attack and the other being the seeming aggro generation of the totem. When I first got the totem I was in a Ragefire Chasm group and I thought I'd test it out on a pull of several troggs. Turns out the second I dropped it, they all ran over and killed my totem, and then me. Frankly, dropping the totem only to see mobs cruise over and annihilate it before it pulses is extremely annoying. I'd suggest holding it in reserve till after mobs are effectively tanked or aggroed on someone else (like a mage or warlock, someone who generates a lot of AoE threat, paladins tanking or what have you) because it's not a terribly cheap totem and it sucks to drop it and watch your mana investment go up in metaphorical smoke.
You want it to go up in actual smoke, preceded by flames. That's why you dropped it, after all.
There is also apparently a glitch that is allowing Fire Nova to proc and damage people of your own faction. I'm not sure how this is achieved, nor am I terribly interested in finding out how to deliberately bug out my own totems to grief my own faction and possibly get a ban for exploiting the game, but it is supposedly happening out there. So if you see a shaman's fire totem in a city you might want to steer clear of it if you have less than 800 health or so.
After you get Fire Nova, your next offensive totem is fourteen levels away. Magma Totem is an effective AoE pulse totem. Like all shaman fire totems, the damage this totem deals isn't equivalent to a damaging spell cast directly by a character, but it's not meant to be: think of these totems as indirect damage over times with reasonable mana costs and an unfortunate tendency to be purged by the enemy taking a second to deal five damage to a stick. Magma Totem's aggro is high enough that you probably won't get much use out of it unless you've somehow ensured that the mobs you're fighting are focused on some other target: you can arrange this by waiting to drop it until a tank or someone else has significant threat, making sure you have significant threat on the targets (Chain Lightning is a good spell for this if you have the time or ability to cast it) so that they'll hit you instead of the totem, or by dropping Stoneclaw Totem first so that it generates threat before the magma pulse does. Unlike any of your offensive totems, Stoneclaw has significantly more health (at level 8, when you first get it, it has 65 health, 13 times that of the three fire totems mentioned here, and by level 67 it has over 1300 health... not significantly hard for a level appropriate mob to kill, true, but compared to magma totem's 5 health at that level it can give the fire totems more time to do their work) and so it won't die in one hit as easily as they will.
Finally we'll mention Fire Elemental Totem. Unlike the previous three totems, which a beginning shaman will have by level 26, you won't see your fire elemental until level 68. On a 20 minute cooldown that it shares with the 'tanking' earth elemental to a small extent (if you summon one elemental you're locked out from summoning the other for two minutes, basically ensuring that a shaman can't have a DPS elemental and tanking elemental up at the same time) the fire elemental totem does exactly what you'd expect from the name and summons a fire elemental. This elemental will cast an AoE similar to the one cast by fire nova as well as run after a hostile target, randomly targeting like searing totem, but rather than spitting a directed fire attack it will punch things. It's rather hilarious on certain bosses to watch the fire elemental run around punching them in the back of the head, and the elemental deals decent damage. I've seen it used to round up a lot of mobs while doing dailies, to burn down dragonhawk spawns in ZA, or to just add more damage to a stubborn boss. The fire elemental can be dismissed by the shaman (by totemic call or just clicking the totem underneath your character bar) and if you were not engaged in combat with whatever the totem was fighting, they won't aggro you, as the totem is not specifically aggro linked to you. If the elemental gets aggro it will probably die pretty fast even if it's being healed, it's not terribly sturdy, but it can deal reasonable damage.
These are the directly offensive totems: there are other totems like Flametongue Weapon that indirectly damage an enemy, but these are the ones that allow shamans a fire and forget capacity: once a totem is dropped, the shaman no longer can or has to direct it in any specific way.
Next week we'll hopefully cover shocks and the lightning spells. Then the week after that we'll cover specific abilities unique to elemental and enhancement shamans.