I started my first game as Drakken, and got the support hero Nachampass. It is past turn 100 and I still can't figure out how to move him out of the capital so that I can fight with him. He's a good governor, but I need him for a quest. How do I do this?

Make an army and when you click at the army there you see in the left corner "assign/attach hero to army"..its quite simple.

Your Hero can't be moved as a single unit, he can only be appointed to an army of your choice. Doesn't matter how many units you have in army - one or six - you can assign your hero to it regardless.

Go to the hero menu. It is the button that looks like a medal; it is located at the top left of the screen amongst the line of different buttons. Click it. It will bring up 'The Academy.' Select your hero and click 'Unassign.' Your hero is now available to be placed on an army or in another city. This makes the now available hero, before being assigned, in a sort of limbo. And yes your hero can only accompany an army, they can not leave on their own. However you can create any army using some units, assign a hero to that army, and then move all those units out of the army. You now have a lone hero as an army to move about as you wish. Also each hero has a 5 turn 'cool down' before they can be made available to unassign and reassign.