Internet Recovery keys are Command+Option+R. If you have installed macOS 10.12.4 or above this key combo will boot to the recovery Utilities Menu and let you install the OS that is currently supported and available for your Mac (e.g. 10.13.3).
Shift+Command+Option+R combo boots to Internet Recovery Utilities Menu so you can install the most current version of the OS that shipped with your Mac (e.g. 10.11.6).
As CountryGirl56 noted, you should be able to boot to something external (e.g. Internet Recovery) and select the Apple HDD HTS.... media (disk) not disk0s2. Run First Aid to see if there are any errors that need to be fixed. Then keep it selected and click Erase to create/format a single volume.