It's covered in the NS Series sensor product guide.
Here's the excerpt:
Connect the cable for Sensor failover
For Sensor failover, connect two NS‑series Sensors using the appropriate cables. These two Sensors
must be running the same software version. The Gigabit port G0/1 is the failover interconnection port
on NS9100 and NS9200 Sensors. The Gigabit ports G1/1 and G1/2 (40G QSFP+) are the failover
interconnection port on the NS9300 Sensor. Failover cables are the only additional hardware required
to support failover communication between two NS‑series Sensors.
1 Plug the cable(s) appropriate for use with your QSFP+ module into port G0/1 (NS9100, NS9200) or G1/1 and G1/2 (NS9300) of the active NS‑series Sensor.
2 Connect the other end of the cable(s) into port G0/1 (NS9100, NS9200) or G1/1 and G1/2(NS9300) of the standby NS‑series Sensor.
The section titled "About connecting cables to the monitoring ports" of the same document covers connecting the networking ports for traffic inspection.
Is there a specific question you have?
Generally in a failover, you want to match the setup on the primary with the secondary so when a failover happens you have the same setup on each sensor.