In this step by step tutorial we will tell how to do a clean installation of Windows 10 using Bootable USB Drive or DVD. The pre-requisite is obviously that you have created a Bootable USB Drive already and you can read our tutorial to learn how to do it.
If you want to perform a clean install on your PC, or if your PC doesn’t have an operating system, you can use the Bootable USB / DVD. Keep in mind that, if you format a drive partition during installation, any data on the partition will be erased. Be sure to back up any data you want to keep before you begin.
Step 1): Turn on your PC, insert the DVD or USB flash drive, and then shut down your PC.
Step 2): Restart your PC, and then press any key to boot from the DVD or USB flash drive.
Step 3): If you restart your PC and your current version of Windows starts, you might have to open a boot menu or change the boot order in your PC’s BIOS or UEFI settings so that your PC boots from the media. To open a boot menu or change the boot order, you’ll typically need to press a combination of keys (such as F2, F12, Delete, or Esc) immediately after you turn on your PC. For instructions on changing the boot order for your PC, check the documentation that came with your PC or go to the manufacturer’s website.
Boot Menu
You will see the next screen. Now choose Windows 10 Setup and hit enter
Windows 10 Boot Manager
If changing the boot menu or order doesn’t work, try again by signing into Windows, shutting down, and then starting your PC.
Step 4) On the Install Windows page, enter your language and other preferences, and then select Next.
Windows 10 clean install 1
Step 5) Select Install Windows.
Windows 10 Install screen
Step 6) On the Enter the product key to activate Windows page, enter your product key. The product key should be in a purchase confirmation email if you bought Windows 10. It looks like this: PRODUCT KEY: XXXXX-XXXXX-XXXXX-XXXXX-XXXXX. Or else you can use this nifty tool to find your product key.
Windows 10 activate key
Step 7) On the License terms page, if you accept the license terms, select I accept the license terms, and then select Next. On the Which type of installation do you want? page, select Custom.
Windwos 10 setup
Step 8) On the Where do you want to install Windows? page, select the partition that you want, select the formatting option you want to perform (if needed), and then follow the instructions. When you’ve finished formatting, select Next.
Follow the rest of the setup instructions to finish installing Windows

https://thewincentral.com/how-to-do-clean-installation-of-windows-10-using-bootable-usb-drive/