To turn your MiFi on, press and hold the Power button for 2 seconds until "MiFi" appears on the screen.

The Home screen lets you see what your MiFi is doing at a glance.

At the top of the screen, you will see status indicators for network signal strength. Four bars or better at 4G LTE is preferred.
Once you see a successful cellular connection status, power on your laptop. Once your laptop connects to the hotspot, the 0 Devices will say 1 Primary.

See the linked Hotspot FAQ document for more detailed information.