So, let me explain
First, all crafting professions have a number of recipes that require one or more Spirits of Harmony. The complete list can be found on Wowhead.
Second, Spirits of Harmony can be used as a currency to buy crafting recipes for Tailoring and Blacksmithing. We have yet to confirm this for other professions, although we can say for sure that there are no Jewelcrafting and Engineering recipes that you can buy with Spirits of Harmony.
Third, Spirits of Harmony can be used as tokens that you can redeem for crafting materials of your choice at your faction's Spirit of Harmony Vendor. For Alliance players, Krystel is located on the terrace of the Shrine of the Seven Stars (the Alliance capital city in Pandaria). For Horde players, Danky is located on the terrace of the Shrine of the Two Moons.
Here is the list of crafting materials you can obtain in exchange of 1 Spirit of Harmony:
- 1x Ironpaw Token: this is a token that you can turn in to Nam Ironpaw at Halfhill Market for Cooking ingredients;
- 1x Restored Artifacts: this is a token that you can turn in to Brann Bronzebeard or Tan Shin Tiao at the Seat of Knowledge for Archeology goodies;
- 1x Starlight Ink: used for Inscription;
- 20x Windwool Cloth: used for Tailoring and First Aid;
- 1x Pandaria Herbs: this bag contains at least 20 herbs from Pandaria that you can use for Alchemy;
- 3x Golden Lotus: used for Alchemy;
- 20x Spirit Dust: used for Enchanting;
- 5x Mysterious Essence: used for Enchanting;
- 1x Ethereal Shard: used for Enchanting;
- 20x Ghost Iron Ore: can be smelted into Ghost Iron Bar and prospected by Jewelcrafters (requires a skill of 500);
- 20x Kyparite: used for Blacksmithing and Engineering, and can be prospected by Jewelcrafters (requires a skill of 550);
- 5x Black Trillium Ore: can be smelted into Trillium Bar and prospected by Jewelcrafters (requires a skill of 600);
- 5x White Trillium Ore: can be smelted into Trillium Bar and prospected by Jewelcrafters (requires a skill of 600);
- 20x Exotic Leather: used for Leatherworking;
- 20x Prismatic Scale: used for Leatherworking;
- 1x Serpent's Eye: used by Jewelcrafters to create their profession-specific gems.