How to use rune stones? (The Witcher 3: Wild Hunt)

You just use it as a weapon (put it on), when you press it, there will be a choice in which weapon / armor to insert.
BUT, for this you must have weapons / armor with empty cells. (black circles are).

Can you point your finger at where these circles are?

GringoBIN
there are mugs on the armor, I think you understand why you can’t insert them into weapons

Understood ATP, why are there no circles on the sword?

GringoBIN
brain man, no means no. Not all equipment in the game with slots for stones