First make the bootable usb: https://forums.macrumors.com/threads/1801963/
Then boot up startup manager with option key.
Then select the usb and bootup from that.
There will be a disk utility there. Use that to erase the drive.
Then quit disk utility and install yosemite to the newly formatted drive.
I've done a clean install before and I don't remember doing anything on terminal. All this just sounds confusing. We're operating on a Mac here man.
First make the bootable usb: https://forums.macrumors.com/threads/1801963/
Then boot up startup manager with option key.
Then select the usb and bootup from that.
There will be a disk utility there. Use that to erase the drive.
Then quit disk utility and install yosemite to the newly formatted drive.
Btw, erase which drive? The macintoshHD drive? Your directions aren't even clear.