We get many questions about runewords in the RoT mod, so on this page I am going to try my best to explain in detail how it works.
Runewords in RoT are comprised of two components, or ingredients, Runes and Socketed Gear (Whether is be armor, or weapons)
In RoT you DO NOT simply right click runes and add them to socketed items like in Vanilla, (at least not to make runewords.) This will add the rune as a component and you will be frustrated, and possibly say things you regret later.
In RoT you make runewords with the Horadric Cube crafting UI.
More information on the Horadric Cube.
You do not need the ingredients your inventory, but you at least need both ingredients in either your stash, shared stash, or inventory for the bench to know you have the right components.
Runewords in RoT have the exact same recipes as in Vanilla. Ex. (Engima is still Jah + Ith + Ber, in a 3 socket armor)
Most, if not all Runewords from Vanilla are in some form able to be crafted. The Devs plan on doing a complete item rework in Patch 0.8.0.0, so note that values may change on items in the future.
Also note that more Runewords may be added. I am not 100% sure on if all the Runewords are here. But I believe they are
The armor and weapon bases able to be used to craft different items are set by the Devs. So you'll notice different types of the same item. Ex. (Caster, Heavy, and Light versions of some items.) These are all technically the same items, But require a different armor or weapon to craft.
Horadric Cube is needed to craft Runewords
You can get Runewords as early as Level 13
Endgame runewords are here to craft.
Everyones all-time favorite leveling Runeword