ToME: the Tales of Maj'Eyal

I cannot figure this out for the life of me. Where do i access the buttons to do this? I am going to feel really stupid when someone explains this to me, it's probably right in front of my face.

Give golem a rune from your inventory or have them pick one up>take control of golem>go to golem's inventory>inscribe rune like you normally would>Voila!