Players may measure distances at any time with no penalty. Some games don't allow pre-measuring, but Arcane Legions does.
When measuring line of sight, for a special ability or for ranged combat, draw an imaginary line from the notch of the originating unit to a notch on its target. This line can't go through the target unit: the target notch must be on a side facing towards the originating unit.
If the line goes through a piece of hindering terrain or another unit, that line of sight is considered hindered. In ranged combat the attacking unit rolls 1 less blue die for each time it is hindered (i.e. for each piece of hindering terrain and each unit between it and the target of the attack).
If the line goes through a piece of blocking terrain, that line of sight is considered blocked. Ranged combat may not be through a blocked line of sight.
Special abilities do not care about line of sight unless they say otherwise.
If a special ability has a range of Within X steps, it affects this unit and any adjacent unit. For example, Aura of Peace affects all units "within 2 steps", which includes the unit with Aura of Peace as well as any adjacent units.