STM32F411RE Nucleo Board save data to flash memory

I have a STM32F411RE nucleo board which I connect to an external button. 
The button is connected via following pins:
+5V, GND and GPIO_PIN_8 (PB_8)
I also have the USART connection to PUTTY.

My code does the follows:
when the button is pressed, the onboard green LED is on. In PUTTY the 
message "button is pressed" is shown.
when the button is not pressed, the onboard green LED is off and in 
PUTTY the message "button not pressed" is shown.

I would like to save the input from GPIO_PIN_8 in some form of file 
either directly on an external drive (microsd oder usb) so that I can 
open it later on. Since the STM32F411RE does not have EEPROM 
functionality, I read that storing data to flash memory is an option. 
Could someone explain to me
a) how can I store data in flash memory
b) how can I "export" data from flash memory to a readable file later on

Any help appreciated, thanks guys