By releasing the energy in a elemental crystal you can fuse or tansmutate ingredients into new items. Creating new items by using crystal energy in conjunction with components from a recipe is called Item Synthesis. Using a crystals engergy to break an item down into one or more components is called Item De-synthesis. Your success at synthesis or de-synthesis is largely based on your crafting skill level.

You must increase your crafting skill levels in order to create high quality or highly sought after items on a regular basis. In order continually increase your crafting skill, you will need to join a guild. Vana'diel is home to nine crafting guilds in which players can join in order to craft (or fish) various items. These guilds are:

• Alchemy
  Uses a wide range of materials to create of a variety of potions and medicines, or weapon enhancements.
• Bonercraft?
  Makes use of animal bones and exoskeletons to create moderately heavy armor and a wide variety of ammunition and jewelry.
• Clothcraft?
  Works with natural threads to craft lightweight armor and capes often used by magic using classes.
• Cooking?
  A craft that combines various spices and ingredients to make a wide variety of enhancing meals.
• Smithing?
  Uses heavy metals to craft super heavy armor and various weapons. Also used to reformulate raw ores into usable ingredients.
• Goldsmithing?
  Works with precious gems and metals to create enhancing jewelry, armor, and weapons.
• Woodworking?
  A craft which works with a wide variety of lumber found around Vana'diel to craft a variety of weapons, ammunition, and furniture.
• Leathercraft?
  Works with animal hides to craft medium-weight and versitile armor.