The first slot unlocks at level 17. There is a total of 6 rune slots, one for each of the six elements. The six elements are: Fire, Earth, Poison, Wind, Lightning, and Ice. Depending on the Element, each rune will provide different bonuses.
The best ways to get runes:
-Completing Survival Instance in an Adventure => Elite Instances Tab every day
-Level 1 Runes can be Purchased in Valor Store
-If you complete most Daily Quests, you’ll get Rune Treasure (chest), it can contain runes level 1-3.
RUNE SET BONUSES
Equipping more than 1 rune of the same level can unlock very powerful rune set bonuses.
Level 2 Rune Set Bonuses are the same as level 3, except 1% less Crit Dam (2% instead of 3%)
Level 3 Rune Set Bonuses:
+2000 HP if you have at least 2 Level 3 runes equipped
+50 Crit if you have at least 4 Level 3 runes equipped
+3.0% Critical Damage if you have all 6 runes equipped, and all of them are level 3
Level 4 Rune Set Bonuses:
+5000 HP if you have at least 2 Level 4 runes equipped
+125 Crit if you have at least 4 Level 4 runes equipped
+4.0% Critical Damage if you have all 6 runes equipped, and all of them are level 4 '
In order to synthesize, you’ll need 3 runes of the same elemental type and level. Then those runes can be merged into 1 Rune that is 1 level higher. For example, 3 Level 1 Earth Runes can be synthesized into 1 level 2 Earth Rune. Every rune type has 8 levels.
Synthesizing Level 1 Runes:
Synthesizing Level 2 Runes:
Synthesizing Level 3 Runes: