Marked Tasks is a visual mechanism that allows a user to identify tasks he/she wants to “follow” closely for a certain period of time. When you mark a task, you are only marking it for yourself and this “mark” (the yellow star) will appear next to the task throughout the interface.
Hint: In “custom” task lists, use the Show/Hide Columns ( icon) to add the “Marked Task ” field to your “Fields to Display”. Then, click on “Marked Task” and add it to your “Sorting Order” by clicking on the button (see image below). Move the “Marked Task” item up in the “Sorting Order” column until it’s the 1st at the top of the list. Then click on “Apply”. Doing this will ensure your marked tasks will appear together at the top of your task lists.