Can you assign right-click skills as 1-2-3-4 keyboard skills?
the Demon Hunter has the skill which can mark an enemy for a 12% damage increase.
Do you have to assign them to the left or right mouse button to mark an enemy, or can I use the keyboard shortcuts 1-2-3-4 to mark?
Start a game, go to Options -> Gameplay and turn on elective mode.
You can then right click any skill slot (or choose the slot on the skill screen) and assign a skill from any category to it. There will be arrows on either side of the bar where the skills are shown for you to scroll between categories.