ZPL is pretty straight forward, and well documented. See the Programmer's manual: https://support.zebra.com/cpws/docs/zpl/zpl-zbi2-pm-en.pdf
If you're new to ZPL, the manual starts off with some simple examples. If you have google-chrome available, there's even a ZPL printer emulator that you can play with here: Zpl Printer - Chrome Web Store
One note about the emulator: If you change the print orientation (e.g. right-to-left), the emulator resets to left-to-right after each print job. The real printer stays in right-to-left mode until either a new print orientation command is sent, or until a printer reset, either power or software.