To boot from a USB drive and install an operating system, ensure the USB drive is connected to your laptop before restarting. Press the key to enter your laptop's BIOS settings (usually F2, F12, or Del) and navigate to the Boot Priority or Boot Order tab. Use the arrow keys to reorder the list, placing the USB drive as the first device in the boot order. Save changes and exit the BIOS settings. Restart your laptop, and it should automatically attempt to boot from the USB drive. If prompted, select the USB drive to boot from. Once booted, follow the on-screen instructions to start the installation process.