Runes are making a comeback in Diablo Immortal! Right now there are a total of 16 different Runes in the Technical Alpha. Runes, however, are nothing but crafting materials in their current iteration; they don't combine into Runewords as they used to in Diablo 2 and have no other additional use-case besides being a crafting ingredient. Furthermore, Runes can not be upgraded with 3:1 upgrade recipe known from Diablo 2. Here is a short overview of all Runes:

All these Runes are automatically stacked in your Inventory just like many other Materials:

Inventory Space for Materials and Runes

Obtaining Runes

Runes drop as a reward at the end of an Elder Rift or your can buy them Marketplace from other Players. Runes are used as a crafting materials at the Apprentice Jeweler to craft Legendary Gems:

Craft Legendary Gems using Runes and Platinum

We know Runes and Runewords are a hot topic in the community, but not much more is known at this stage of the Alpha - Stay tuned!