Once you have your macOS Sierra 10.12 DMG, you need to "burn" it to a USB drive (minimum 12GB).
Finding a "repack" on third-party sites can be risky due to malware. It is always recommended to try official channels first: mac os sierra 1012dmg download repack
Are you planning to install this on an or a virtual machine ? Once you have your macOS Sierra 10
macOS Sierra 10.12 DMG Download: The Guide to Repack and Installation mac os sierra 1012dmg download repack
A "DMG" is a disk image file used by macOS to distribute software. A typically refers to a modified or compressed version of the original installer.