How do you eat from a shared tagine?

The short answer

Right hand, bread as utensil, eat from the section in front of you.

The left hand is considered unclean. Tear a piece of bread (khobz) and use it to scoop. Eat from the section directly in front of you, working inward. Don't reach across. If your host pushes a piece of meat toward you, that's generosity — accept it.