When creating the task through quick add on the Tasks tab, type an exclamation point at the end of the task name. Example: This is my priority task! When the task is added, it will show a gold star to the right of the space picture indicating it has been marked as a priority task.
When creating the task through the green [+] button under the My Kona logo you can type in the exclamation point at the end or click the star icon at the top to mark a task as a priority.
You can remove the priority at any time by clicking on the gold star of the task or in the details of the task itself.