Every time your PC turns on, for a slight second it shows you what keys you could press to do something else rather then just turn in on.
Since you're trying to boot from a drive (USB or CD) you want to enter a boot order settings. Every PC opens a boot order settings with a different key, but it's ussualy ESC, F12 or F2 keys. Pay close attention to the information your PC provides to you when you turn it on. If it will help, reboot it few times, it really won't hurt the computer. Once you've successfully opened the boot settings, with keyboard arrows navigate to the drive you're trying to boot from (eg USB DRIVE) and press Enter.
To enter BIOS pay attention to the information your computer gives you every time you turn it on. Ussualy it's the Delete button. So when you turn on your PC, press the Delete button repeatedly until you enter the BIOS. In there, you'll have to navigate your way to boot order settings. It's not the same process for every computer but here's an overview:
Follow these steps:
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