To play Contra Rebirth as a ROM on your computer:
Download an NES emulator like Nestopia, FCEUX, or Jnes.
Obtain a Contra Rebirth ROM file (ensure it's from a legitimate source).
Open the emulator and load the Contra Rebirth ROM file.
Configure the emulator's controls to your preference (keyboard or gamepad).
Start the emulator, and Contra Rebirth should begin running.
Enjoy playing Contra Rebirth on your computer, using the emulator to emulate the original console experience.