The Matrix is your existing task priorities laid out on the classic urgent/important grid — there's no second field to fill in. Urgent tasks land in "Do first", High in "Schedule", Medium in "Delegate", and Low in "Eliminate".
It's a way of looking at the same tasks you already have, not a separate list — change a task's priority anywhere in Abledo and it moves to a different quadrant here automatically.
The Matrix is off by default. Turn it on from Settings → Navigation if you don't see it in the sidebar.