1. Turn off the laptop.
2. Connect the USB.
3. Press and hold the F11 button, then turn on the laptop (while still holding the F11 button).
You can see how to do it in this video:
If the F11 button does not work, please try:
1. Disconnect all other devices and ensure that the AC adapter is plugged in.
2. Connect an external device to your VAIO computer. Press the ASSIST button while your VAIO computer is off.
3. The VAIO Care (Rescue Mode) screen appears. Select Start from media (USB device/optical disc).
4. The booting process from the external device starts.