A bow or throwing weapon can be equipped in addition to any melee weapon and/or shield.
Arrows or Quiver of Arrows must be equipped in order to use the bow, and a bow must be equipped in order to use the special arrows.
The number that appears after Magic+ is the amount of extra damage that the weapon does (as shown in the Damage field in the character info screen.) For more info on the Damage field see the manual.
Notation:
Icon/Name/Scenario/Damage Vs. Small/Vs. Large/Weight