Shaman have three main styles:
- Face Tank: They tank, probably slow (except at low levels when slow is terrible and not worth the mana), and deal melee, pet, and DoT damage
- Pet Tank: Same as above except they root the mob and let their pet tank instead; in exchange for some mana and their melee damage they get to meditate, cannibalize, deal with other mobs, etc.
- No Tank (Root Rot): Same as above except both melee and pet damage is lost; in exchange healing mana is saved, and possibly also slow mana, though at higher levels slow is often still used for safety on root breaks
Throughout your entire Shaman career you will be switching between these three styles, because there is no "right" one. The correct one
for a given situation depends on factors such as:
- your level: obviously it matters what spells you have at your disposal and whether you even have a pet
- how hard the mob you're fighting hits: hard hitters should be root/rotted, weaker ones tanked
- how much HP the mob has: mobs with lots of HP mean long fights, and in long fights the difference between how much damage you take and how much damage your pet takes becomes more noticeable, making pet tanking potentially worse for high HP mobs (or better I guess, if you're on a corpse run with no gear)
- whether the mob casts: pet tanks generally work well against casters, as the pet keeps agro on itself, preventing the mob from casting on you ... but against wizards your pet might die too quickly; also most Shaman are large which means they can use Slam to interrupt casts, but only if they tank
- whether the mob summons: root/rot isn't even an option on them
Other than that it's just minor variations like don't use long-duration DoTs on low HP mobs. Do a few quick test fights with/without Frenzy to see how much damage it really adds for the mana, and then only use it if it actually matters. That sort of thing.
Others can probably give better advice specific to your level, as it's been awhile since I was that level. FWIW I remember a whole lot of root/rotting with only occasional meleeing thrown in, even though I had a Barbarian Spiritist's Hammer for a lot of it (and this was pre-proc nerf so it was better then than it is now). But ultimately you just want to decide which style to use for the current mob based on ... the current mob.