Gems are used for advancing gear. Gem can be an alternative if you don’t have the gear to advancing gear. Gems can be obtained at the shop. Shop> exchange> gear
Gem there are 2 types, amplification gem and honor gem
Amplification gem used for advancing grade sr gear and below at lv 20, 40 and lv 60.
Honor gem used for advancing grade ssr gear and below at lv 20, 40 and lv 60.