Connect the DK or dongle to your computer and turn it on. Then place it between the Central and Peripheral device that you want to sniff.
Note
If you are using a DK with the nRF Universal Serial Bus (USB) connector available, it is recommended to use the nRF USB connector instead of the virtual COM port of the onboard interface MCU. This is because the virtual COM port cannot match the higher Bluetooth LE throughput of the nRF USB connector.
Proceed to running the nRF Sniffer.