Ok, here come some spoilers. If you don't want to be spoiled, don't read.

This phase of the event is simply elemental attacks all over the world. There is nothing to do with them except destroy the rifts they come out of, you get a buff for this, nothing else. The quests are available at any level, and include you running around a capital city, and the surrounding zones.

The next phase will have elementals directly attacking the city. The first phase has you securing the city from flooding (SW), reinforcing the city (IF), or setting up barricades (Orgrimmar). Second phase all of the NPC's in the town that didn't evacuate are frozen. You have to run around and unfreeze them. Third phase you have to destroy the elemental rifts in the city. The elementals that pour out of the rifts are level 80. You will be killed unless you use one of the evacuation portals around the city if you are a lowbie. Once the rifts are closed, two rifts open up, and allow you access to one of two of the event bosses. These portals are available for a half hour after the event. The event repeats every few hours. The entire city will be unusable while the event is going down.

I am going to have to correct myself here. There is a quest with the elementals, from looting an object from the rift. Never encountered that during the PTR, so didn't know about it.