In Clash Of Crystal, you may loot different sorts of Gems. Once you receive equipment with a socket, you can inlay Gems into this equipment to improve its quality.
1. Open your bag (B) and go to the Socket tab.
2. Insert your equipment. If there is no socket in your equipment, you will need a Socketing Rod. You may either buy it from the Item Mall or loot it from a variety of monsters.
3. Select an empty space to create a socket in your equipment.
4. Drag your Gem into the socket and you are done!