Charlie is having a romantic dinner with a very sensuous draconian when his cel phone rings. Still, it's pretty funny to have leader hero Charlie who is not in the battle apply a suffocation spell on an elf lord across the map. Then again, you can cast with a leader hero that is not in the battle. So, if you cast with one of Baker's spells, you could still move and attack with Alpha. Pick the tab for the hero for the spell you want cast. You can do that with the big cast-o-spell button that's in the lower right menu.

If you select the cast spell button in Baker's menu, you can cast one of Baker's spells. So, Alpha is the leader, but it's Baker's turn. If you have heroes in the battle, you can cast directly from that hero. You need at least one hero to cast a spell, but the hero does not have to be part of the battle. Once you are out of spell points, you can't spend any more mana. That's how much cost you can throw in one tactical match. Then there are spell points, the gold stars. That's how much 'money' you can spend on casting spells. There are mana points, the little blue crystal flowers. I'll probably miss or forget something, but maybe this will get you started:

Age of wonders 3 good combat heroes