Every task has a status which can be determined by its icon. The task statuses are: Not Started, In Progress, Completed, On Hold, and Canceled.
To change the status of a task, tap the icon for the task, then select the new status. Tasks can be accessed from Task List and Task Calendar under Tasks + Projects, or from My Calendar. Tasks that have been associated with topic objects can also be accessed directly from the detail view for those topic objects.