Hello beluga and welcome to the forum
I myself do not know the controller key assignment. But you can read it in the system menu under control (esc key).
You equip a role like any spell (roles can only be used once). You equip spells in the magic menu. You have to click and mark roles in the inventory first. Then the spell is equipped in the left or right hand (as with spells). Then you can use it and "fire" it.
It is different with the teleport rolls. They are always equipped in both hands (but the game does this automatically).