There are five different types of runes that can boost your character into some particular stats.
Additional Runes option will be unlocked once complete set of runes are equipped on your gear.

#1 .





Runes can be made by using Synthesize Window

Providing significant amount of gems for each Runes.

Upgrading runes requires another set of Gems and so on.

Adding Runes on any part of your gear requires no cost but there is still a chance of failing and breaking your runes. (Items won't break upon failing, only Runes)

Simply click Forge > Runes

Unlocked Rune Option