OS deleted

If necessary, purchase Snow Leopard, update it to 10.6.8, and then use the posted download link to install El Capitan.

Snow Leopard Purchase    

Use the combo update to save time in Software Update.

10.6.8 Combo Updater

App Store Update for OS X Snow Leopard

Which Mac? An eMac is a PowerPC-based Mac from the early 2000s, and the commands and sequences that far back do differ from those on more recent Macs.

Are you looking to some restore existing backups, or to install a fresh copy of macOS?

If booting from Recovery is not working, then a download of El Capitan, High Sierra, or Mojave onto another local Mac would be common, and then create a bootable USB installer (with related instructions) on that other Mac, and then transfer that USB installer over to the target Mac, and boot that.

If there's a backup available, then the Migration Assistant can be used to restore those files after the re-installation.

It's also possible to use this sequence to restore a Time Machine backup.

The iMac (Early 2008) tops out at El Capitan. Download the installer and generate the bootable installer on another Mac, if Recovery is not working here. (See previous reply for links.)