I am playing through the beginning campaign scenarios, and I cannot figure out how to get my elven archers to attack from range. Defensively I have seen them defend adjacent units, but I cannot figure out to get them to use range.

IIRC ranged units attack like all others, but if a ranged unit attacks a non ranged unit, the non ranged unit can't strike back because they get attacked from afar.
If a ranged unit attacks another ranged unit then bith units deal damage.

Edit
The manual says:

Missile Units
Archers and Bombardiers use their missile rating when attacking. These units stand at
long range and fire bows, rifles, or in the case of Bombardiers, drop rocks, or burning oil.
Like Skirmishers, Light Cavalry, and Spellcasters, these units avoid hand-to-hand combat.
Their Melee and Missile ratings are reflective of this. When a Archer or Bombardier unit
attacks it can only be attacked in return if the defending unit has a Missile rating. If an
Archer unit is attacked then it is forced to the attacker’s range of engagement.
Bombardiers can only be forced to Melee range by Sky Hunters. Otherwise they may
only be attacked by Archers, Siege Engines, or units who have a Missile rating.

Yep, I read that in the manual, but I can only get the starting elven archers to attack like melee units. In other words, the unit must be directly next to defending unit. When two hexes away, I see no option for attacking. Just a normal cursor.

Thank you.