To turn the unit on, look for the power button, located on the side of the unit. Momentarily press the circular button and after a couple of seconds you will see the Atomos logo and then the home screen.
To turn the unit off, touch "menu" on the home screen, and then press the red Power off icon for 3 to 4 seconds. The icon will go white when touched to indicate activation of the button and then the unit will power off. Alternatively you can also do a forced power down by depressing the physical on/off button on the side of the unit for 3 to 4 seconds. Holding it down for a few seconds is intentional to ensure you don't inadvertently power down the unit during recording.
Pressing the on/off button for a short time (less than 3-4 seconds) activates the "lock/unlock" mode rather than the power down sequence. To power down after locking the screen, simply unlock the screen by again momentarily pressing the on/off button and then do the correct shut down sequence as described above.