For opening Ahn’Qiraj both Horde and Alliance have to collect thousands of supplies to aid in the war effort. You could turn these in at the War Effort bases (located at the Military Ward in Ironforge for Alliance, and the Valley of Spirits in Orgrimmar for Horde).

Each turn-in gives you  Ahn’Qiraj War Effort Supplies, containing a green item equivalent to the level of the item you have turned in, and a number of signets ( Alliance Commendation Signet /  Horde Commendation Signet), which can be turned in at Commendation Officers for reputation.

Both factions have to gather a total of:

90,000  Copper Bar (1 signet per turn in)

26,000  Purple Lotus (7 signets per turn in)

80,000  Thick Leather (7 signets per turn in)

17,000  Spotted Yellowtail (7 signets per turn in)

400,000  Runecloth Bandage (10 signets per turn in)

Alliance have to gather:

180,000  Light Leather (1 signet)

800,000  Linen Bandage (1 signet)

110,000  Medium Leather (3 signets)

33,000  Stranglekelp (3 signets)

14,000  Rainbow Fin Albacore (3 signets)

28,000  Iron Bar (5 signets)

20,000  Roast Raptor (5 signets)

600,000  Silk Bandage (5 signets)

24,000  Thorium Bar (10 signets)

20,000  Arthas’ Tears (10 signets)

Horde have to gather:

96,000  Peacebloom (1 signet)

10,000  Lean Wolf Steak (1 signet)

22,000  Tin Bar (3 signets)

250,000  Wool Bandage (3 signets)

19,000  Firebloom (5 signets)

60,000  Heavy Leather (5 signets)

18,000  Mithril Bar (7 signets)

250,000  Mageweave Bandage (7 signets)

60,000  Rugged Leather (10 signets)

10,000  Baked Salmon (10 signets)

Once supplies are collected, the ten-hour-long continent-wide event begins. Obelisks Resonating Crystal Formations reportedly appeared in Silithus, Tanaris, Feralas, The Barrens, Darkshore, Thousand Needles and Un’Goro Crater. These obelisks spawn different creatures to kill.
There are also 3-time limited delivery quests available in Cenarion Hold during this 10-hour event. Each quest rewarded 2 70, as well as  Colossal Bag of Loot.