In order to activate the kiosk mode on a Chromebox, please follow these steps:

Turn on the ChromeBox
Select language, keyboard region and network connection.
Press continue.
Accept the terms and conditions.
At the “enter email address” screen, press Ctrl + Alt + k
Click on “Enable” and then click on OK.

Chrome OS - Automated Kiosk Mode

Now we enter our email account and password
We already have the ChromeBox ready in kiosk mode.