If you press on the dot next to the task, it will turn blue and pin the goal to the top of the list. Starred goals are priority goals.
You can use this to mark a goal as your top priority for now. You can use it to separate your most important commitments from the rest of the goals. Or you can mark goals that you want to track the progress of but you are not necessarily the person who is working on them. All starred goals are added to the 'Starred' menu and can be viewed from there.
It is an easy way to set a priority and keep track of an important goal your team is working on.