You already have a bootable flash drive.
How to do this is described in this – article
Boot from a flash drive.
How to boot from an external USB device is written in this article
1. After you first boot the computer you’ll see a screen like this one. Choose the OS’ language, time and currency format, and input method.
2. Click Next and you’ll be taken to the Install now button screen. Which obviously you should click.
4. Select type of installation. As we are doing a clean install, we should choose the custom install (files, settings, and apps aren’t moved).
5. At this point you’ll need to pick where to install Windows 10. You might need to delete or create a partition.
6. Wait while Windows installs. This process may take anywhere from half an hour to several hours, depending on your computer’s previous operating system and processing speed.
After the installation is complete, the computer will restart, do not forget to remove the boot from the flash drive or you can just pull out the flash drive.
7. Create an account. Type a username.
8. Create a password. You can skip this step and do it later.
9. Enter your Windows 10 key, then click Next
10. Click “Use recommended settings”
11. Choose time zone, date, time
12. Set network location. if you are not sure, select public network.
13. After loading the desktop select the Start button, then right click on Computer > Properties
14. Click Activate window now
IMPORTANT! You must be connected to the Internet!
15. Click Activate window online now
15. Congratulations your Windows is activated!