The Sensors Tab will be enabled if you have an On-Premise Enterprise Sensor (either a Virtual Machine or a Hardware Sensor). A sensor is required for each ingress/egress point to the internet that you want to monitor.
In the Sensors Tab you can view all your sensors in one place.
If you choose the sensor from the list and view details you can see the Local DNS, look at the sensors Alarms and Events and also get a One-Time Password to configure the sensor (for setting a static IP if required).
You can also manage what SysLogs you have pointed to the sensor.
You can also choose to view all the Netflow stats on each individual sensor.