Blizzard posted a preview of Battle for Darkshore warfront which will start in the hands of the Forsaken, and Horde by extent, but Alliance will attempt to reclaim the lands Sylvannas burned, plagued and took from the Night Elves.
Alliance players will need to be maximum level, 120, and complete Tyrande's new storyline in order to kick the Darkshore warfront off. Night Elves will be the exception to this rule, and they will be immediately able to queue for the warfront, most likely because it is their land they are fighting for.
In case of Battle for Darkshore, the cycle has been shortened in the first two weeks so the players can earn its rewards before the Holiday Season. Considering this is the second warfront to be added, players will be able to contribute either in Darkshore or in Stormgarde. Progress in either warfront is completely independent of the other, so players can earn rewards on both sides.
The way contributions work will be changed for Stormgarde, to match that of the newly introduced Darkshore, so instead of the previously 11 available quests in the contribution phase, players will get three quests each day. One will be a turn-in of either gold or War Resources, while the other two will be profession turn-ins.
Siege phase will be somewhat different in Darkshore due to different units, locations, objectives, etc. Minimum gear score requirement will be 320. Players who enter at this level will stand to gain better gear as Battle for Darkshore will award gear that starts at level 340.
The objective of the Alliance will be to reclaim the land and rejuvenate it, while Horde will take upon the role of environmental enemies and try to keep it devastated so Night Elves can't use it.
As for rewards, players will be able to earn Night Elf or Forsaken-themed armour sets, depending on which faction they play in. Service Medals will be among the rewards, which can be used for the further glorification of Azeroth's fashionistas. You can read about the new warfront in detail on the official website.