Ranged is a skill that determines how much damage you can deal with a Ranged weapon. These include Bows, Crossbows, and Knives. This skill also determines which ranged weapons you can use (See Bows, Crossbows, Knives). Some Agility shortcuts require a higher Ranged level to use Grappling hooks.
Some areas to train your Ranged Level:
Minotaurs (Level 27) - First level in the Stronghold Of Security.
Ogres (Level 53) - South of Castle Wars
Ogres (Level 63) - Caged, in the Camelot Train Camp. (Requires Biohazard Quest)