To apply a label to your task, click the check box next to the task(s) to which you wish to apply the label. Click the Label icon, and then type the name of the label into the Apply Labels box. You can select several tasks at one time, and add the same label to all tasks. Be sure to hit the Apply Label Changes button.
If you only have one task that needs a label, hit the label icon just to the left of the task and add the label quickly.
A task can have more than one label if needed. Once you add the label, you can now quickly organize your tasks by using the applied labels.