please explain these, I want to underesatnd it

RCC_APB2ENR |= 1 << 5;

RCC_APB2ENR |= 1 << 3;

GPIOD_CRL = 0x33333333;

GPIOD_CRH = 0x33333333;

GPIOB_CRL=0X44444444;

GPIOB_CRH=0X44444444;