Shocks are a shaman’s instant cast direct damage spells (DD). The three different shock spells all have a secondary effect. Using the correct shock at the right time can make a huge difference in a fight. All shocks share the same cool down timer of six seconds. This can be lowered with talent points.
Earth Shock
Earth shock is the first shock you get; it is obtained at level four, and ranks up as appropriate. Earth shock does okay direct damage for the mana cost. Earth shock is considered a nature spell for resistance and casting reasons. The secondary effect of earth shock is that it interrupts spell casting and makes it so that spells of the same school as the spell interrupted cannot be cast for two seconds. Earth shock is used to counter magic. If fighting a player or mob that relies on spell damage as its main source of damage, you should be only using earth shock to interrupt the spells. Save the cool down for when it counts.

Flame Shock
Flame shock is obtained at level 10 and ranks up as appropriate. Flame shock does good damage for the mana costs. Flame shock is considered a fire spell for resistance and casting reasons. The secondary effect of flame shock is a damage over time (DoT) effect. This is what makes flame shock so mana efficient. The burst damage of flame shock is not high, but the overall damage this shock causes for the amount of mana it costs makes it the most efficient of shock spells. The DoT effect can also keep rouges from vanishing. The DoT will tick and bring the rogue out of stealth. Flame shock should be used if you don’t need to counter spell the target or snare it.
Frost Shock
Frost Shock is obtained at level 20 and ranks up as appropriate. Frost shock is an expensive spell to cast, but has high burst damage. Frost shock is considered a frost spell for resistance and casting reasons. The secondary effect of frost shock is a snare effect, which reduces the targets movement speed by 50% for eight seconds. Frost shock is commonly used to kite a target. With the spell lasting longer than the recast time, you can effectively kite the target until it is dead without casting any other spell. Frost shock is very useful to stop runners in battle grounds, and NPCs that run on low health, if frosh shock doesn’t kill them. Frost shock is one of the shaman's most useful spells.