You can access the Tasks relating to a particular Progress Tracker on a particular project or album by launching the Tasks Popup on a Board.
The Tasks Popup lets you:
Create a Task
Complete a Task (i.e. mark it as Done)
See the To Do list of tasks
See the list of Done tasks
How to create a Task
Find the Card you want to create a Task on
Click the Tasks button on that Card
The Tasks Popup launches
Type the Task into the text window
Press More Options to assign the task to a particular person
Press Save Task