The update addresses the critical KRACK (Key Reinstallation Attack) vulnerability that affects Wi-Fi WPA2 protocol security.
Once you have the DMG file and a properly formatted USB drive, you can follow the standard Apple method to create a bootable installer.
Shortly after 10.13.1's release, a serious security flaw was discovered allowing anyone to gain root access by entering "root" as the username with a blank password.
Once you have the DMG (or the "Install macOS High Sierra" app), follow these steps to create a bootable drive: Plug in a USB drive with at least 12GB of space. Open Terminal and use the createinstallmedia command. It typically looks like this: