bow can't put to sword position & can't use in it position; only boxing
First, equip the crossbow. Do this by going to your inventory and dragging the bow to the "ranged weapon" slot.
Second, equip the bolts.
press and hold Tab to bring up the quick menu, and select the crossbow (it should be at the bottom of the circle)
When in combat, hold the middle mouse button to aim, and let go of the mouse button to fire.