Each time a ranged attack is made against an INFANTRY unit with this tenet, if the attacker is not within Engagement Range of that unit, models in that unit receive the benefits of Light Cover against that attack (see the Warhammer 40,000 Core Book).
If you selected a Tactical Philosophy (pg 92) at the start of the battle, T'AU AUXILIARY units that are in the same Detachment as units with this tenet benefit from your army's selected Tactical Philosophy.
Building an army? Create, validate and share your list with New Recruit, army builder for Warhammer 40,000 9th Edition and many more games.