I played IA a while back, about four missions in, but since I hadn't played in a while and got a boatload of new content (at 68% of all content vs. just the base game) I decided to play the tutorial mission tonight.

I moved the initial Stormtrooper group, no problem, but when it becomes the heroes 1st turn, their portraits are surrounded by a black circle, and when I attempt to click their portraits to indicate they've activated, I hear a noise, but that's it.

What am I missing to activate heroes?

SORRY for the newbie question.

Did you end the stormtrooper activation? There's a button that you can click to tell the app you're done with them. It's under where it tells you how they move and attack.

The tutorial has some bugs. Check that you don't have any dialog box active that is asking for your input and that the activation window of the imperial unit isn't "minimized". (View Map minimizes the imperial activation window. You need to click it back to end the imperial activation.)