PICKING TARGETS
First, you must pick the target units for the attacks.
In order to attack an enemy unit, an enemy model from that unit must be in range of the attacking weapon (i.e. within the maximum distance, in inches, of the Range listed for the weapon making the attack), and visible to the attacker (if unsure, stoop down and get a look from behind the attacking model to see if the target is visible).
For the purposes of determining visibility, an attacking model can see through other models in its unit.