Casting Spells

To cast any spell, first open the Major Units Information Window and don't close it.
Casting Attack Spells: To cast an attack spell, switch to the local map and select an enemy stack. Then bring the Major Units Info Window to the front and click on the spell. Attack spells cost a fixed rate regardless of how large the enemy stack is.
Casting Bless Spells: To cast an bless spell, switch to the local map and select an friendly stack.  Then select the units you wish to cast spells on from within the stack list.  Then bring the Major Units Info Window to the front and click on the spell.  In the Spell List is a cost column. Bless spells are 'charged' per unit.  So Heal costs one point per unit selected. Three Units selected, three points.
Casting Other Spells: There is only one 'other' spell right now and it's Clairvoyance.  Select the cell you want to see, then click the Clairvoyance spell out of a Major Unit's Spell List. That square and all adjacent squares will become visible to you.  Unlike attack and bless spells, Clairvoyance is not limited by the magic users range.