Gems and Runes
Gems and Runes are both "components" in RoT, much like any of the other Grim Dawn components.
To use a Gem or Rune as a component: Right-click the gem or rune, and left-click the item you want to use it on.
More Information on Runes for Runewords
Gems and Runes can be upgraded or downgraded (Yes you read that right) with the Horadric Cube.
So different from Vanilla, if you have a Zod and need a Cham, you can downgrade 1 Zod into a Cham.
You can still upgrade too. Have 2 Cham and need a Zod? No worries, the Cube has the power!
Have a Perfect Ruby, but leveling so you need a Flawless Ruby instead? You can downgrade it!
Have a ton of Flawless, but need a Perfect? You can upgrade them!
They(As in both gems and runes) can only be added to Body Armor, Weapons (Both 1 handed and 2 handed), shields, off-hands, and Helmets.
So along with being used to make runewords, you can also use a rune as a component on that said runeword!
Gems come in all different styles with all different stats, explore what is best for your build!
Runes follow the same drop table as Vanilla Diablo, like zone requirements, Countess drop table ( Normal: El - Ral, Nightmare: El - Io/Ko ; above Io is much rarer, Hell: El - Ist/Lo ; above Ist is much rarer.), etc.
High runes drop more frequently at higher levels. So you never have to be, and shouldn't be worried about crafting end game gear. You'll find that Ber you need for Chains of Honor, I promise!
Gems & Runes come in all different types.
A Collection on Gems
All Runes from DII are currently in-game