sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume --applicationpath /Applications/Install\ macOS\ Sierra.app
See the Apple Support page here : https://support.apple.com/en-us/HT201372
or watch this video
TIP: You will probably need to erase the HDD using the disk utility before installing.
If you do, chose what ever name you like, one of the Mac Formats and make sure to choose the GUID scheme.