God of War Ragnarok has 8 Chaos Flame Locations. They are used to upgrade the level of the Blades of Chaos, one of your weapons. The Blades start at Level 1, using 8 Chaos Flames upgrades it to Level 9 which is the maximum (Level 1 Starting Level + 8 Chaos Flames = Level 9).
You can use the Chaos Flames at the Blacksmith to upgrade the Blades of Chaos. This also increases your average equipment level as seen in the top left corner of the Weapons Menu. The higher your overall level, the more powerful you become. Each level also increases the damage of the blades.
You get all Chaos Flames automatically while going for 100% Completion. The majority is dropped by mandatory story bosses. If you forgot to loot one, the item is automatically placed in the blue chest at the blacksmith and can be retrieved from there.
Other Weapon Upgrade Materials:
All 8 Chaos Flames
Chaos Flame #8
Reward for doing all 6 Draugr Holes. Each gives a Chaos Spark, the 6 Chaos Sparks together form 1 Chaos Flame.
That’s all 8 Chaos Flames to fully upgrade the Blades of Chaos.
For everything needed to reach 100% Completion check out the God of War Ragnarok Wiki & Strategy Guide.