You need to get into the BIOS boot order setting,
When you start up your computer there is an screen that dhows the maker of the computer and on it there is a note of how to get to the BIOS. When there look fo Boot order or Boot menu. Make sure the USB was plugged in before restarting. In the Boot order move the USB listing to the top and the you can reboot and it will boot the USB stick.
After installing Windows 10 you will need to go back into the BIOS and make the HDD or SSD the first one on the list.