We recommend using either NFC Tools or NFC TagWriter by NXP.
This should bring you through to the next screen which should allow you to select "New Dataset" or "Add a Record".
Here you can input various fields of data to write to your tag.
After you are finished inputting all of the data that you wish to write, save your data and move onto writing.
Hold the card up to the back of your phone and wait for the app to confirm that the data has been successfully written onto the card.
You can then test your NFC card by tapping it against your phone and waiting for it trigger a prompt.
iPhones:The reader should be on the upper half of the phone.
Android phones:The reader can either be on the center or the upper half, depending on the model.