When you click on the Actions menu, a label tab appears (click for a detailed explanation), where you can create new labels for your campaigns, name groups, and keywords. You can then use these labels for various purposes.
It is possible to categorize the labels you create and change their colors.
Once you click labels in the actions menu a box similar to the one shown above will display. You'll find all of your previously saved labels there. You can create new labels and categorize them according to your preferences.
Using labels actively saves you a lot of time, allows you to do your campaign management in a more planned way, and to observe the performance effects.
Once you label certain items, in order to display them you can filter by label.
There you have it!