Booting while holding the shift key (no other keys, just the shift key) will boot a Mac to Safe Boot mode.
It will not allow most startup software, but will give you a basic system. It's one way to see if your system has a chance of working. If you did actually delete some part of your installed system, then it's likely that safe boot mode won't work, either... And, you will need to let Internet Recovery finish booting. It can take some time for that, as it is booting completely from an Apple remote server. I had a 2011 iMac that took nearly 15 minutes to get there.
If Internet Recovery does not eventually finish (or you don't want to wait), then your only real choice is to boot to an external USB drive, with a system installed, or a bootable USB drive with a macOS system installer on the drive.
If you do need help with that, just post here, and someone will help, or at least give you a link with more information.