What is the meaning of this?

i need help dont know whats the meaning of this.

void zero()
{
  PORTD = 0b01111110;
}

void one()
{
  PORTD = 0b00001100;
}

void two()
{
  PORTD = 0b10110110;
}
}

what is the meaning of the 0b01111110 , 0b00001100 , 0b10110110

Those are binary constants:

You will also sometimes see them written like B01111110 in Arduino. The reason was that when Arduino started GCC didn't have the binary constants so Arduino defined their own:

Thanks man!