Arduino for STM32

I'm using STM32F401RE, with core Arm Cortex-M4

How can I pass through the serial ports an arduino number to the STM32 F401RE? Using the Arduino IDE? For now I have done this:
(i should do all this using just the arduino ide)

Code Arduino (TX)

int valueTX=5;

void setup() {
Serial.begin(9600);
}

void loop() {
Serial.print(valueTX ...