When the ZIP file has finished downloading, it's time to boot your device into custom recovery mode. (android.gadgethacks.com)
Now, you need to select the «Recovery» option with the help of Volume down button and select it by tapping the power button to boot the device in the recovery mode. (androidadvices.com)
This file will be very useful in case you can not boot your device after installing the new files. (android.gs)