Gemming Guide
Right click a gem to open this window or press the "regrade item" button in your inventory and press the lunagem tab at the top.
NOTE: The 100% slot chance after the first 2 slots ONLY applies for Toughness and Resilience gems which go into your leg and chest armor.
Once you upgrade out of Soulforged gear, your goal should be to fill the slots with all T4 (pink gems)