Can I get a free copy of OS X from my Macbook Pro's serial number or something? I'd like to reinstall macOS on this computer.
1 Answer
The cost of macOS is included with the Mac. You can reinstall using either Internet Recovery or a bootable USB installer.
Apple's brief description is How to reinstall macOS.
Depending on the state of your boot disk, you will probably not be able to use simple Recovery Mode (Command-R when powering on), but will need one of the choices under "Other macOS installation options". Easiest may be Internet Recovery (command-option-R when powering on).
Using a bootable USB installer requires another Mac to download macOS and to create the bootable USB.