How to set thumbnails label?

Hi @ponlyhong!

You should go to the thumbnails settings:
http://doc.smartslider3.com/article/80-thumbnails
And there you should turn on the Caption – Title option, maybe the Description too. Also under them you will be able to choose the “placement” for these texts, where I think you will need the “After” option.
After this you will see the “name” and the “description” at your thumbnails, what you have gave to your slides:
http://doc.smartslider3.com/article/394-slide-settings