By default, tasks are displayed by due date, with the oldest tasks at the top of the screen, and the newest tasks at the bottom, so that those tasks due first will display first. However, you may have a particular task that you would like to appear higher on the list. You can accomplish this by assigning the task a priortity.
Next to each task name is a white box with a series of gray stars in in it. You can point and click on any of the stars to prioritize your tasks. Tasks with a 5-star rating will appear higher on your list than tasks with a 1-star rating.