have 2009 iMac that was totally erased and want to reinstall high Sierra, what do I need to do ?

Only a late 2009 iMac supports macOS 10.13 High Sierra. See if you can boot into Internet Recovery Mode using Command + R or Command + Option + R.

If you have access to another Mac compatible with macOS 10.11 or 10.13, then you can create a bootable macOS USB installer:

https://support.apple.com/en-us/HT201372

Or you can use the original OSX 10.6.x Snow Leopard DVD that originally shipped with your iMac.

Just curious why you didn't click "Install macOS" after quitting Disk Utility after erasing the drive?