My MacBook Air comes originally with El Capitan.
I call to Apple Support because I want install a clean macOS Sierra, and they told me Hold Command+R, delete the Hard Disk, and next Select Reinstall.
By default the connection was Wifi. The problem, this connection is very slowly, I haven't option to select my thunderbold LAN connection, instead of Wifi.
The Wifi for me its vey problematic, and I need to reboot. Then appears world globe... After I delete my HD again, but Appears El Capitan.
The problem this methods needs 10 hours over a problematic wifi.
I think that I need to install El Capitan later upgrade to Sierra Later again repeat the procedure (delete HD & Format) to perform a Clean installation of macOS Sierra.
Is there a Quickly method?
Is recommended Alt over Command+R?
How can I to select Thunderbolt LAN connection by default to install macOS?
Note: I haven't runnable macOS now in My MacBook!
NOTE: I have a macOS Sierra installer on USB External Hard Disk (Original & Modified), but I don't know how install directly from USB.