The number displayed on each button shows how many projects/tasks currently match that category, giving you a live snapshot of where your workload stands. Select a quick filter button to apply it — the grid will update to show only the matching projects/tasks. You can apply more than 1 quick filter at the same time; for example, selecting both
Overdue
and
No due date
will show projects/tasks that match either category. Select an active filter button again to remove it.