As soon as you hear the startup chime press and hold the option key on your keyboard. Installation Instructions:Insert the USB in your USB Slot.
Please be patient and allow the process plenty of time to finish.
This USB can be used to install a clean copy of Apple Mac OS x snow leopard 10.6 or to update your existing system to Mac Os x snow leopard 10.6 Installing, Recovering or upgrading your software from a USB is NOT a quick process and can take 30-45 minutes to complete.