Athena's healing touch affects all allied units and buildings in a small area. As long as the light shines down, units in the area will regain hitpoints.

To use Restoration, left click on the Restoration icon, then target anywhere on the map.  Using Restoration during a fight can prolong the life of your armies.  Using it while a town is under attack can save your buildings.

"Of Pallas Athena, guardian of the city, I begin to sing. Dread is she, and with Ares she loves deeds of war, the sack of cities and the shouting and the battle. It is she who saves the people as they go out to war and come back. Hail, goddess, and give us good fortune with happiness!"

-- Homeric Hymn to Athena