To use a Dubai Nol Card, simply touch the card to the reader at the entrance of the bus or metro station. The fare will be deducted from the balance on the card. When exiting, touch the card to the reader again. For buses, there is no need to touch the card when boarding or exiting.
If you are using the card for multiple trips, be sure to check the balance before each ride. You can do this by touching the card to the reader at any fare gate. The remaining balance will be displayed on the screen.