Question mark appears after resetting through macos Recovery

I tried the following steps below but my screen still appears with a question mark. Please help.

Shut down your Mac, then turn it on and immediately press and hold these four keys together: Option, Command, P, and R. You can release the keys after about 20 seconds, during which your Mac might appear to restart.

• On Mac computers that play a startup sound, you can release the keys after the second startup sound.