The first thing you need to know about this event is that you don't need to own The War Within™ expansion to take part. This event will take place on July 31, one week after the release of the Prepatch. You need to be Level 10. Also, to complete the prepatch questline, you must first complete the Harbinger questline. You'll set off from Dalaran, the hub where you'll find the event's vendor, as well as the portals to access the various zones involved. These are Dragonblight, Dustwallow March, and Searing Gorge. The time before an event recurs in one of these zones will be 90, 60, and 30 minutes respectively, for the first, second, third, and fourth weeks.

Step 1: A first boss can be killed to trigger the rest of the event.

Step 2: Defeat 6 Radiant Echoes in the zone, an indicator on your interface, as well as map markers, will keep you informed of the stage's current progress.                                               

They can be bosses to kill, items to collect, actions to perform, and so on, this stage is pretty cool if you've been playing Wow for awhile, bringing back memories of iconic quests and bosses from Wow's history.

Step 3: A zone boss appears (The Lich King, Onyxia or Ragnaros, depending on the zone). Don't forget to take the quest available near the zone portal, which requires you to kill this last boss to be rewarded with additional currency, please note that if you are not present during the fight, the quest will not be credited, and you will have to wait for the next event in the same zone.

Step 4: The event is over as soon as the boss dies, Radiant Echoes remain until the next rotation (90, 60, 30 minutes). They allow you to farm the event currency until the next zone.

Rewards

As with any prepatch event the equipment you obtain is primarily intended to catch up with the iLvl of your late rerolls, so you’ll be able to buy 480 items, which can be upgraded to tackle the expansion in late August.

You'll also be able to obtain pets, mounts, a 32-slot bag, as well as a new Heirloom ring, created by merging essences from the event’s 3 zones with the “receptable” ring sold to the intendant of Radiant Echoes.

As for the Heritage ring, it's relatively simple, completing Radiant Echoes scenarios in stage 2 will occasionally grant you Memories of the Collecting 20 of these will enable you to merge them into the Essence of this zone, merge the essences of the 3 different zones with the event intendant's “receptable” ring, and you’ll get your new Heirloom ring.