Start by making sure the target computer is shut down.
Insert the USB into an empty slot. Keep the option key pressed down (third button from the bottom-left) and turn on the computer. Keep pressing the button for about 5 seconds until a screen with a white background with at least two icons are showing up.
Release the button once this menu has showed up.
If you see the Apple logo instead of this menu, you’ve gotten too far and you need to try again by turning off the computer again.
Search for the icon with the text “EFI Boot” and click on it. Ignore the error messages showing up during the startup. Once the software has started up and you’ve reached the Lockero main menu you can choose language and keyboard layout (usually same as your language). If you want to connect through WiFi, you can select your WiFi name in the dropdown list, enter the password and click on Connect. 
When the status has changed to “Connected”, you can then click on Next. Click here to return to the main guide.