Arduino for STM32

I have a code for Arduino UNO that uses port manipulation. However, the code does not compile for STM32 Nucleo F103RB. The error says that the Ports are not defined.

What does a code like:

PORTB = (PORTB & B11111100) | ((d) & B00000011);

mean and how can I translate it to make it work with my Nucleo board?

you need to review the ref manual rm0008

and a google search would bring up the related example codes and materials e.g.
https://www.google.com/search?q=stm32+g ... a+register
http://fastbitlab.com/gpio-input-data-register/
http://fastbitlab.com/gpio-output-data-register/
https://gist.github.com/iwalpola/6c36c9 ... 0a118571ca
https://controllerstech.com/stm32-gpio- ... registers/

STM32 have 16 port per register so you'll need to change Arduino code to account for that.

Output registers are GPIOx->ODR (eg. GPIOA->ODR)
Input registers are GPIOx->IDR